vegetation and climate history of northern japan inferred from the 5500 year pollen record from the oshima peninsula sw hokkaido this study reconstructs middle and late holocene vegetation and climate dynamics in the oshima peninsula sw hokkaido using the published method of biome reconstruction and modern analogue technique applied to the yakumo pollen record 42 17 03 n 140 15 34 e spanning the last 5500 years two previously published matrices assigning japanese plant pollen taxa to the major vegetation types biomes are tested using a newly compiled dataset of 78 surface pollen spectra from hokkaido with both matrices showing strengths and weaknesses in reconstructing cool mixed and temperate deciduous forests of hokkaido the results suggest the necessity to consider the whole list of identified terrestrial pollen taxa for generating robust vegetation reconstructions for northern japan applied to the fossil pollen data both biome reconstruction approaches demonstrate consistently that oak dominated cool mixed forest spread in the study region between 5 5 and 3 6 cal ka bp and was subsequently replaced by beech dominated temperate deciduous forest the pollen based climate reconstruction suggests this change in the vegetation composition was caused by a shift from cooler and drier than present climate to warmer and wetter similar to modern conditions about 3 6 cal ka bp comparing the pollen based reconstruction results with the published marine records from the nw pacific the reconstructed vegetation and climate dynamics can be satisfactorily explained by the greater role played by the warm tsushima current in the sea of japan and in the tsugaru strait during the middle and late holocene an increase in sea surface temperatures west and south of the study site would favour air temperature rise and moisture uptake and cause an increase in precipitation and snow accumulation in the western part of hokkaido during the late holocene

latest quaternary oceanographic changes in the okhotsk sea based on diatom records abstract the okhotsk sea is a locus of the north pacific intermediate water formation today the formation of the okhotsk intermediate water is linked with seasonal sea ice cover diatom records from the okhotsk sea show the following 1 during the last glacial maximum between 21 000 yr b p and 18 000 yr b p sea ice covered the western side of the sea throughout the whole year but the eastern part was open this permitted more efficient heat exchange with the atmosphere than waters and hence ventilation of the glacial okhotsk sea waters which in turn caused a greater extent of intermediate water formation through the bussol strait 2 the perennial sea ice cover extended northward and sea ice was present throughout the whole year over a great part of the sea except for the eastern part between 18 000 yr b p and 17 000 yr b p 3 the ice free area extended greatly to the south during the interval between 17 000 yr b p and 11 000 yr b p 4 there was no perennial ice cover over the whole sea and the ice free area that appeared as the seasonal ice area began to extend to the western part between 11 000 yr b p and 8 000 yr b p 5 after 8000 yr b p the ice free waters contracted to the present extent

diatom derived ssts td ratio indicate warm seas off japan during the middle holocene 8 2 3 3 kyr bp abstract regression analysis was performed between the ratio of warm and cold water diatoms td ratio in 123 surface sediment samples in the northwest pacific ocean and the mean annual sea surface temperatures ssts c at the core sites in order to calibrate this proxy for paleo temperatures equations to derive annual sst c from diatom analysis were somewhat different for the tohoku area y 6 5711 0 273 r 0 89946 than for the japan sea y 5 4069 0 26841 r 0 89088 the annual paleo ssts c in the tohoku area were in general higher than in the japan sea despite lower td values because the warm water species fragilariopsis doliolus is abundant only in the tsushima warm current in the japan sea the reliability of the equations is supported by our understanding of the ecology of recent diatoms td derived annual paleo ssts c agree with alkenone derived summer paleo sst c at a site off central japan in the northwestern pacific in a south to north transect of cores around honshu and hokkaido paleo ssts c decreased when the kuroshio and tsushima warm currents weakened the middle holocene 8 2 3 3 cal kyr bp was warmer by 1 2 c than earlier and later parts of the holocene and mean annual paleo ssts c show rhythmic fluctuations with durations of 1000 years and 400 500 years these new data show that annual ssts were warm in the northwestern pacific at times that the northeastern pacific was cold in addition oceanic warm and cold water species defined by kanaya and koizumi kanaya t koizumi i 1966 interpretation of diatom thanatocoenoses from the north pacific applied to a study of core v20 130 studies of a deep sea core v20 130 part iv sci rep tohoku univ 2nd series geol 37 89 130 and koizumi et al koizumi i irino t oba t 2004 paleoceanography during the last 150 kyr off central japan based on diatom floras mar micropaleontol 53 293 365 are illustrated

coastal management and sea level rise abstract the predicted rise in sea level due to global warming has given rise to much speculation as to the impact on erosion and accretion rates at the coast as well as increases in hazards to coastal users this paper focuses on the spatial adjustments that coastal landforms will exhibit in response to changing energy gradients both normal to and parallel to the shore these adjustments in many cases will take the form of the migration of landforms in order that they maintain their position within the coastal energy gradient prediction of the rates of such migration will be fundamental to the future management of the changing coastal environment the paper discusses the impact of sea level rise on the two basic coastal landform assemblages those in estuaries and those on the open coast and then goes on to examine the effect on ebb tidal deltas that are located at the critical junction between estuaries and open coasts in each case the rates of landform migration under an accelerated sea level rise are predicted and compared with existing rates using examples from the east coast of britain assuming a sea level rise of 6 mm year the paper predicts that estuaries will migrate landwards at rates of around 10 m year open coast landforms can exhibit long shore migration rates of 50 m year while ebb tidal deltas may extend laterally along the shore at rates of 300 m year the implication for the management of such dynamic coastal systems including such issues as coastal defence and conservation are discussed

paleoceanographic evolution of north pacific surface water off japan during the past 150 000years abstract hydrographic variability in the mixed water region of the northwest pacific ocean at latitudes 35 40 n between the kuroshio extension and oyashio front causes complex upwelling leading to large primary productivity and thus great fishery resources we reconstructed the periodicity of the variability in north pacific intermediate water upwelling and surface ocean hydrography based on the high resolution analysis of diatom assemblages in seven cores representing the last 150 000 years we derived annual sea surface temperatures ssts through a diatom based proxy td the td derived annual ssts c are controlled by orbital forcing and show a reversed saw tooth in southern cores in contrast to a normal saw tooth pattern in the northern cores oceanic diatom abundances along the northern margin of the mixed water region are twice times as high as beneath the axis of the kuroshio extension and fluctuated in a revised saw tooth pattern with higher overall abundances interglacials after the last deglaciation annual ssts declined markedly during heinrich and bond events in the northern north atlantic when ice rafted detritus transported by icebergs was abundant wavelet analyses of the record of oceanic diatom abundances show significant variability at 2 0 kyr 2 to 5 6 kyr and 3 2 to 9 6 kyr periods wavelet analyses of the annual sst records show significant periodicity at 1 4 to 2 6 kyr 3 3 to 4 0 kyr 7 2 to 12 8 kyr cycles

varieties of a single cosmopolitan diatom species associated with surface water masses in the north pacific abstract a time series of 65 sediment trap samples representing 48 month changes in diatom flora and 62 sediment core tops from the western north pacific ocean were analyzed varieties of a single diatom species were found to be characteristic of two surface water masses bounded by the kuroshio current thalassionema nitzschioides var incurvata var inflata and var parva dominate in warm saline waters in the subtropical gyre while t nitzschioides sensu stricto is abundant in less saline waters northwest of this current time series data on percent abundances for the three t nitzschioides varieties in the t nitzschioides complex are compared with path variations of the current south of japan inter annual fluctuations in percent abundance are linked to changes in surface water masses over the sediment traps in association with migration of the kuroshio paths this finding makes the percent abundance a useful tool for deciphering path migrations of the kuroshio current in the geologic past down core analyses of two sediment cores collected beneath the modern kuroshio current were performed a sharp increase in percent abundances from 12 to 9 kyr bp with an abrupt change around 11 kyr bp records the previously reported transition of the kuroshio current from a predominantly offshore path to its modern path path migrations of the kuroshio current may be inferred from percent abundances of these diatoms which comprise a new proxy for delineating the paleoclimate of the northwestern pacific in relation to changes in northward heat transport from the western equatorial pacific ocean by the western boundary current

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

paleoceanographic history around the tsugaru strait between the japan sea and the northwest pacific ocean since 30 cal kyr bp abstract the paleoceanographic history around the tsugaru strait since 30 0 cal kyr bp was reconstructed using ecological and biogeographical habitats of diatom species and q mode factor analysis of diatom flora in six piston cores at 30 0 17 5 cal kyr bp a fall in sea level and the intensification of the oyashio current caused erosion of submarine sediments near the shore in the eastern area of the strait and led to deposition of the third and second sequences of thinly laminated layers tl3 and tl2 in the japan sea at 17 5 11 5 cal kyr bp cooling intensified around the strait producing an inflow of oyashio water into the japan sea through the strait at 15 5 14 5 cal kyr bp a cold water mass around the strait developed from subarctic sea ice to arctic waters at 13 0 11 2 cal kyr bp the younger dryas cooling was clearly recorded by the increasing of oceanic cold water diatom species in the eastern area of the tsugaru strait but not in the japan sea at 15 5 13 0 cal kyr bp and 11 25 10 25 cal kyr bp the warming around the younger dryas resulted in the deposition of thinly laminated layers off shimokita in the eastern area of the strait at 9 5 cal kyr bp the oyashio current water intruded into deep depths in the mixed water region off sanriku at 9 5 7 0 cal kyr bp the fluctuation of 1 5 kyr intervals in the strength of the tsushima warm current system in the japan sea was initiated

pliocene pleistocene evolution of the north pacific ocean atmosphere system interpreted from fossil diatoms the relative abundance of diatom taxa in 216 core tops has been quantified and compared using cluster analysis with assemblages in six cores located beneath different water masses of the north pacific ocean all but one sequence span at least 1 5 m y early pleistocene to holocene and one extends to 2 6 ma the quantitative abundance of each taxon and the space time occurrence of each cluster are interpreted as tracers of oceanographic conditions in addition to high frequency glacial interglacial oscillations the records display rapid steplike changes at 2 4 ma 1 6 1 5 ma 1 0 ma 0 8 0 7 ma and 0 35 ma two secondary transitions recorded only in the northwestern cores occur at 2 0 ma and 1 1 ma we conclude that both the high frequency oscillations and the stepwise transitions reflect variations in extent of subarctic water masses under the influence of the siberian high pressure and aleutian low pressure atmospheric cells we further conclude that 1 the subarctic water mass has developed progressively and attained its modern structure only in the late pleistocene 2 some stages of this evolution may have occurred earlier in the eastern subarctic 3 the holocene is an atypical warm extreme so that the present is not a very good key to the past 4 there were several glaciations between 2 4 and 2 0 ma and 5 the subtropical gyre is more conservative than the subarctic gyre and major changes in the region have been due to forcing from the north we propose a conceptual model of oscillating metastable climatic modes maintained by internal feedback and suggest that steplike changes may occur when one set of boundary conditions is temporarily exceeded

fine grained sediment budget on the continental margin of the bay of biscay abstract under present day conditions rivers are the main source of fine sediments dispersed to the bay of biscay they deliver about 2 5 10 6 t yr 1 of continental fine sediments 60 of which is derived from the gironde estuary of this flux 65 is believed stored on the shelf two kinds of mud fields can be found in the bay of biscay coastal mud and shelf mud belts the total mass of fine sediments stored during the past 2000 years is 3 2 10 9 t consequently about 0 9 10 6 t yr 1 could reach the shelf edge and eventually the open sea from this amount of displaced material and the deposition surface areas an evaluation of sediment fluxes across the margin during the late holocene period is discussed this evaluation is compared with results obtained from ecosysteme du canyon du cap ferret ecofer data from sediment traps and surficial box cores

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

a three dimensional hydrodynamic model of estuarine circulation with an application to southampton water uk abstract a three dimensional hydrodynamic model has been developed to simulate water mass circulation in estuarine systems this model is based on the primitive equation in cartesian coordinates with a terrain following structure coupled with a mellor yamada 2 5 turbulence scheme a fractional step method is applied and the subset of equations is solved with finite volume and finite element methods a dry wet process simulates the presence of the tidal flat at low water river inputs are introduced using a point source method the model was applied to a partially mixed macrotidal temperate estuary southampton water uk the model is validated by comparisons with sea surface elevation adcp measurements and salinity data collected in 2001 the mean spring range 2 m2 s2 and the mean neap range 2 m2 s2 are modelled with an error relative to observation of 12 and 16 respectively the unique tidal regime of the system with the presence of the young flood stand corresponding to the slackening conditions occurring at mid flood and double high water corresponding to an extension of the slackening conditions at high tide is accurately reproduced in the model the dynamics of the modelled mean surface and bottom velocity closely match the adcp measurements during neap tides rms of the difference is 0 09 and 0 01 m s 1 at the bottom and at the surface respectively whereas at spring the difference is greater rms of the difference is 0 25 and 0 20 m s 1 at bottom and surface respectively the spatial and temporal variation of the degree of stratification as indicated by salinity distributions compares well with observations

long term weakening of the east asian summer and winter monsoons during the mid to late holocene recorded by aeolian deposits at the eastern edge of the mu us desert abstract the east asian summer monsoon easm and east asian winter monsoon eawm are major drivers of environmental conditions in east asia however due to the lack of high resolution eawm records the phase relationship between the easm and eawm during the holocene epoch is still debated here we use magnetic and grain size measurements from a sequence of aeolian sediments from the eastern edge of the mu us desert to track the history of the easm and eawm from 7 5 to 2 5 ka the results show that both the easm and eawm exhibit a similar long term weakening trend during this interval in view of the stable glacial boundary conditions and the significantly decreased rates of atmospheric co 2 rise since the mid holocene we suggest that orbitally induced insolation was the major cause of the weakening of both the easm and eawm decreasing summer insolation and increasing winter insolation reduced the thermal contrast between the ocean and the asian continent in both summer and winter time resulting in the weakening of both monsoon systems during the mid to late holocene

holocene stalagmite oxygen isotopic record from the japan sea side of the japanese islands as a new proxy of the east asian winter monsoon abstract stalagmite oxygen stable isotopic records from chinese and japanese caves have described the intensity of the east asian summer monsoon easm in the late quaternary in this study we present a stalagmite 18o record over the past 10 000 years from fukugaguchi cave itoigawa honshu japan facing the japan sea the regional climate is characteristically wet in winter and nearly 60 of the annual precipitation occurs from november to march when the east asian winter monsoon eawm brings moisture from the japan sea warmed by the tsushima warm current rainwater 18o values near the cave generally decrease with the precipitation amount indicating an amount effect the stalagmite 18o profile has had a concurrent trend with winter precipitation observed near the cave since 1924 in addition to high resolution records of the eolian fraction observed in china these agreements suggest that the fukugaguchi stalagmite 18o record reflects the eawm intensity in comparison of our profile with the easm record obtained from chinese stalagmites inverse correlation was recognized only in the earlier interval of 10 0 5 2 ka suggesting that the southward migration of the intertropical convergence zone intensified the eawm from a peak at 5 2 ka the eawm intensity quickly decreased and remained at a lower level between 4 5 and 3 0 ka since 3 0 ka the fukugaguchi record has high amplitude changes of millennial time scales including two peak intervals in 2 9 2 5 ka and 1 3 0 7 ka eawm related winter precipitation might have been amplified with intensification of the tsushima warm current that enhanced the land sea thermal contrast during winter season a co variation presumed between the fukugaguchi 18o record and the chinese eawm records implies that the thermal contrast between east asia and nw pacific may have influenced the winter monsoon in throughout the east asian climate system

hydrodynamics and sedimentation induced by large scale coastal developments in the keum river estuary korea abstract the macro tidal keum river estuary located in the eastern yellow sea has been suffering siltation and morphological change since 1994 to understand the effects of the large scale coastal developments on the sedimentation processes in the estuary hydrodynamic and sedimentary data collected from 1985 to 2002 were analyzed and numerical experiments of hydrodynamics were performed the sedimentation rate in the estuary increased by a factor of 1 9 from 3 5 10 6 to 6 7 10 6 m 3 y 1 after the construction of a dam in the upper reaches of the estuary in 1994 large part of the estuary is veneered by the muddy sediments noticeably which were rarely found before dam construction since then siltation has concentrated in the upper estuary rather than the lower the upstream transport and accumulation of fine grained sediments is due to 1 the change to flood dominance in the main channel i e the relative intensification of flood current and the flood directed residual current and 2 the decrease in transport capacity in the upper estuary i e the marked decrease in current velocity which was induced by dam construction the former has resulted in the ebb dominance of the gaeya channel a distributary in the north of the main channel the tidal pumping of fine sediments was reinforced not by the freshwater saltwater interaction but by the residual tidal circulation the sediment fluxes observed in 2001 2002 demonstrate year round net inflow both at the entrance of the jetties and at the gaeya channel which implies that the sediments delivered by the keum river are entirely confined to the estuary incapable of escaping to the sea the net inward transport of fine sediments may accumulate pollutants adsorbed to or absorbed in the sediment grains in the estuary thus deteriorating the benthic environment gradually and the water quality eventually

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

distinguishing natural evolution and human impact on estuarine morpho sedimentary development a case study from the vilaine estuary france estuaries are coastal areas controlled by hydrodynamic factors such as sea level changes waves and tidal currents and river discharge this study focuses on the vilaine estuary which is strongly impacted by human activity after construction of arzal dam in 1970 the purpose of this research is to differentiate the role of natural from anthropogenic factors on sediment dynamics within the vilaine estuary we are proposing a hypothetical model based on the hydrodynamic modification and morpho sedimentary development by analyzing the natural estuarine evolution and the impact of human alteration to the natural system by utilizing datasets including river discharge tidal currents winds and wave activities to further combine with photographic bathymetric topographic and sedimentary surveys results show that waves carry sediment from the sea and rework local sediments the river damming is reducing the tidal prims and leads to the fall of tidal currents this new situation supports the sediment deposition and reduces at the same time the accommodation space which decrease tidal currents in feed back the vilaine estuary is therefore coming close to a bay type functioning which leads to a channel narrowing a drastic increase of the tidal flat zone an acceleration of erosional processes affecting the main channel salt marsh and all associated depositional systems we propose a hypothetical model showing that this evolution took place in two steps and we show that the dam has an effect to accelerate a natural infilling of the estuary

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

the dynamics of a partially mixed estuary measurements of velocity density and pressure gradient in the lower hudson river estuary were used to quantify the dominant terms in the momentum equation and to characterize their variations at tidal and spring neap timescales the vertical momentum flux assumed to be due mainly to turbulent shear stress was estimated indirectly based on the residual from the acceleration and pressure gradient terms the indirect estimates of stress compared favorably to bottom stress estimates using a quadratic drag law supporting the hypothesis that the tidal momentum equation involves a local balance between tidal acceleration pressure gradient and stress divergence estimates of eddy viscosity indicated that there was significant tidal asymmetry with flood tide values exceeding ebb values by a factor of 2 as a consequence of the asymmetry the vertical structure of the tidally averaged stress bore no resemblance to the tidally averaged shear in spite of the asymmetry of vertical mixing the tidally averaged estuarine circulation was found to depend simply on the intensity of bottom turbulence which could be parameterized by a rayleigh drag formulation based on the tidal velocity magnitude and the tidally averaged near bottom flow this seemingly paradoxical result indicates that the estuarine circulation can be modeled without detailed knowledge of the effective eddy viscosity only requiring an estimate of the bottom drag coefficient the tidal forcing conditions and the baroclinic pressure gradient a notable characteristic of this solution is an inverse dependence of the estuarine circulation on the amplitude of the tides

out of phase evolution between summer and winter east asian monsoons during the holocene as recorded by chinese loess deposits we analyzed climate proxies from loessic soil sections of the southern chinese loess plateau the early holocene paleosol s0 is 3 2 m thick and contains six sub soil units co eval soils from the central loess plateau are thinner 1 m consequently higher resolution stratigraphic analyses can be made on our new sections and provide more insight into holocene temporal variation of the east asian monsoon both summer and winter monsoon evolution signals are recorded in the same sections enabling the study of phase relationships between the signals our analyses consist of i measurements of magnetic properties sensitive to the production of fine grained magnetic minerals which reflect precipitation intensity and summer monsoon strength and ii grain size analyses which reflect winter monsoon strength our results indicate that the holocene precipitation maximum occurred in the mid holocene 7 8 3 5 cal ka bp with an arid interval at 6 3 5 3 cal ka bp the winter monsoon intensity declined to a minimum during 5 0 3 4 cal ka bp these results suggest that the east asian summer and winter monsoons were out of phase during the holocene possibly due to their different sensitivities to ice and snow coverage at high latitudes and to sea surface temperature at low latitudes

centennial to millennial scale change of holocene shallow marine environments recorded in ostracode fauna northeast japan abstract using the record of shallow marine ostracode fauna and sediment grain size data from an 865 cm long piston core obtained from mutsu bay northeast japan paleoceanographic changes of the bay were determined at high resolution for the early to middle holocene changes in the relative frequencies of several species showed periodicities of 1300 1800 years similar to bond cycles at around 10 300 cal yr bp and again at 9500 9300 cal yr bp cold water strongly influenced the bay owing to cooling events since at least 10 200 cal yr bp the tsugaru warm current influenced the surface waters and since ca 7400 cal yr bp also the bottom waters of the bay since ca 8400 cal yr bp the water depth rapidly increased and peaked at 7000 5900 cal yr bp due to global sea level rise subsequently a drop of water temperature and sea level in the bay at 5900 and around 4000 cal yr bp influenced the composition of the ostracode assemblages these millennial scale oscillations in relative sea level and bay temperature during the holocene can be correlated to paleoclimate records elsewhere

two long and pronounced cold periods 3 000 5 000 and 6 600 8 400 years b p in east asia and the southward migration of the westerly jet abstract to reconstruct the variations in sea surface temperature sst during the holocene the alkenone unsaturation index of marine sediments from two deep drilled cores and 81 different core top surface sediments recovered from the heuksan mud belt located off the southwestern coast of the korean peninsula was measured first comparison of the alkenone temperature estimates of 81 core top sediments with in situ temperatures indicated that the alkenone temperatures corresponded to the average sst in april to october the spatial distribution pattern of the core top alkenone sst showed a north south temperature gradient which represented the in situ temperatures well this indicated that the effects of the resuspension and lateral transport of sediments on the past temperature estimation might be insignificant based on the two deep drilled cores variations in the alkenone sst during the holocene were reconstructed in general the alkenone sst decreased by less than 1 c from the early to late holocene an interesting feature was the presence of two long and pronounced cold approximately 2 c periods which occurred at 3 5 kyr and 6 6 8 4 kyr b p these cold periods were also observed in other mid latitude regions in east asia indicating that the cooling pattern was regional the cold periods appeared to be associated with the southward migration of the westerly jet at that time investigations into the effects of local sea level changes and resultant changes in the tidal regime on changes in the sst during the holocene period suggested that they were insignificant in the study area

climatic solar oceanic and geomagnetic influences on late glacial and holocene atmospheric 14c 12c change late glacial and holocene 14c12c ratios of atmospheric co2 vary in magnitude from a few per mil for annual decadal pertubations to more than 10 for events lasting millennia a data set illuminating 10 to 104 yr variability refines our understanding of oceanic climatic versus geomagnetic or solar forcing of atmospheric 14c12c ratios most of the variance in the holocene atmospheric 14c12c record can be attributed to the geomagnetic millennia time scale and solar century time scale influence on the flux of primary cosmic rays entering the atmosphere attributing the observed atmospheric 14c12c changes to climate alone leads to ocean circulation and or global wind speed changes incompatible with proxy records climate ocean related 14c redistribution between carbon reservoirs while evidently playing a minor role during the holocene may have perturbed atmospheric 14c12c ratios measurably during the late glacial younger dryas event first order corrections to the radiocarbon time scale 12 000 30 000 14c yr b p are calculated from adjusted lake sediment and tree ring records and from geomagnetically defined model 14c histories paleosunspot numbers 100 9700 cal yr b p are derived from the relationship of model 14c production rates to sunspot observations the spectral interpretation of the 14c12c atmospheric record favors higher than average solar activity levels for the next century minimal evidence was found for a sun weather relationship

coral reefs at 34 n japan exploring the end of environmental gradients we describe the architecture and development of the highest latitude coral reefs currently known on earth located in japan at 34 n the reefs are distributed within turbid inner bays and undergo winter sea surface temperatures ssts that fall to 13 c well below the generally accepted lower limit 18 c in winter of tropical coral reef formation despite low ssts and high turbidity coring indicates reefs ranging to 555 cm in thickness since ca 4 3 k y ago the reefs exhibit high adaptability to this extremely marginal environment variability of the tsushima warm current and the asian monsoon could have affected the evolution of these reefs the corals are dominantly faviids in contrast to acropora and porites that tend to dominate low latitude tropical subtropical reefs defining the end of the distributional range the reefs serve as baselines for understanding coral reef distribution along sst and turbidity gradients

last glacial emplacement of methane derived authigenic carbonates in the sea of japan constrained by diatom assemblage carbon 14 and carbonate content abstract we studied diatom assemblages and caco 3 contents of methane derived authigenic carbonates from the eastern margin of the sea of japan and assessed the formation time of these samples radioactive 14 c date was determined in selected samples to obtain the maximum age of the time the results of our study suggest mass formation of carbonate nodules in a glacial period within 40 ky consistent with a published u th dating result of carbonate nodules in the study area diatom assemblages and contents in the carbonate nodules abundance of 10 6 g dominance of neritic littoral species warm cold water species ratio lower than 25 differ from the near seafloor sediments in the study area which have characteristics of holocene sediments in the sea of japan and suggest cementation of glacial sediments laminated sediments in some nodule samples are glacial sediments because laminations are records of a low sea level period in the semi enclosed ocean similarity of diatom assemblages and contents in all carbonate samples is another evidence of glacial sediments in nodules glacial sediments with oceanic cold water species as low as holocene sediments restricts the sediment age to before 20 cal ky bp carbonate contents higher than 78 wt suggest the cementation of poorly compacted sediments near the seafloor and the date of carbonate cementation is therefore close to that of the cemented sediments most carbonate nodule samples in this study were formed in a glacial period and detection of 14 c restricts this period to within 40 ky

distribution and modification of north pacific intermediate water in the kuroshio oyashio interfrontal zone abstract a multiship ctd survey was conducted in the kuroshio oyash interfrontal zone in the area of 30 41 n 140 e 180 from may to june 1992 to examine the distribution modification process and formation site of north pacific intermediate water npiw low salinity oyashio water and high salinity kuroshio water merge along the kuroshio extension just off the east coast of japan and together flow eastward eastward geostrophic transport and salinity across the kuroshio strong current indicate that the mixture of the kuroshio and oyashia waters along the kuroshio extension can produce new npiw transport estimate suggests that the new npiw bifurcates into the interfrontal zone and into the recirculation of the subtropical gyre a salinity minimum structure can he also created due to the isopycnal mixing along the kuroshio extension between the oyashio and kuroshio waters which have different salinity and vertical velocity structures the low salinity oyashio water seen along the oyashio branches and t

a multi disciplinary study of frontal systems in the tay estuary scotland the results of a remote sensing study of tidal mixing processes in the tay estuary have been correlated with the results of mathematical and physical models and ground sampling data in an attempt to assess the nature the spatial and temporal extent and the variability in the formation of convergent fronts in the tay estuary the application of remote sensing methods to the study of estuarine mixing processes in the tay estuary supported by ground measurements has discovered convergent front mechanisms and complex hydrodynamic processes which had not previously been recognized in the tay estuary this integrated approach has enabled the various features and mixing mechanisms found in the lower section of the estuary to be interrelated the limitations of using a two dimensional mathematical and a physical model to predict the complex mixing processes affecting water quality in the tay estuary are discussed

diatoms in northeast pacific surface sediments as paleoceanographic proxies abstract fossil diatom total abundances valves g in 54 surface sediment samples from the northeast ne pacific ocean reflect the position of high primary production associated with coastal upwelling and that possible biases associated with dilution or dissolution are small diatom species assemblages defined by q mode factor analysis in 30 samples with abundant diatoms are related to modern oceanographic properties five statistical assemblages given by five specific diatom species and or groups are related to upwelling chaetoceros spores subtropical thalassionema nitzschioides subarctic rhizosolenia hebetata transitional neodenticula seminae and freshwater freshwater diatoms ecological environments these factors are significantly correlated with primary productivity temperature nutrient concentrations and salinity although the strongest relationship is that between diatom assemblages and productivity however it is not possible to distinguish between coastal and open ocean curl driven upwelling based on chaetoceros spores relative percentages by themselves or on the floral factors

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

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

changes in storminess and surges in western france during the last century french meteorological data provide some information on wind direction since 1890 since 1951 wind speed and direction have been digitised every three hours in many stations the brest tide gauge has recorded hourly sea levels since 1860 thus enabling hourly surges to be calculated and studied this set of data has been organised into a data base and analysed in order to recognize evolution and trends strong winds are increasing in frequency in the western part of brittany and decreasing in normandy and pays de loire surges associated with these winds do present a slight decreasing trend a more precise analysis allows to distinguish between southerly winds which are slightly decreasing and strong winds from other directions which display a more or less important increase in frequency the analysis shows trends that may be linked to the global circulation pattern and that result in a new spatial distribution of winds on western france

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

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

rapid human induced siltation of the macro tidal ord river estuary western australia field studies on the sediment dynamics of the two arms of cambridge gulf tropical western australia were undertaken the system is macro tidal with 8 m tides the west arm is the estuary of the durack and pentecost rivers which are largely untouched by human activities the east arm is the estuary of the ord river affected by land clearing which started 100 years ago and by two river dams constructed 30 years ago prior to damming of the ord river the natural flow in all rivers was highly seasonal characterized by small at times negligible flow during the dry season which lasts eight months and occasional river floods during the wet season which lasts four months the river flow has been regulated in the east arm as a result of damming this resulted in suppressing large river floods the salinity intrusion length has decreased by about 50 in the east arm following river damming the east arm has silted measurably over the last 30 years with the stream cross sectional area decreasing by about 50 field and numerical studies suggest that this is due to the dam induced suppression of large river floods which has in turn allowed a greater amount of tidal pumping of sediment into the east arm from cambridge gulf since tidal pumping is increasing as the system is silting the east arm appears to now be geomorphologically unstable as a result of human activities numerical studies suggest it may take as little as 100 years for the ord river to reach a new equilibrium modelling suggests that this equilibrium may be characterized by a salinity intrusion length half that before damming a channel width and depth reduced by 70 and a much stronger tidal asymmetry characterized by an increasing size of the tidal bore the west arm appears to be at equilibrium since there has been no net loss or gain of sediment for the last 111 years tidal dynamics and river floods appear responsible for self scouring this channel

transgressive systems tract of a ria type estuary the late holocene vilaine river drowned valley france the understanding of control parameters of estuarine infilling at different scales in time and space is important for near future projections and better management of these areas facing sea level change during the last 20 years the stratigraphy of late quaternary estuaries has been extensively investigated leading to the development of depositional models which describe the sedimentary facies distribution according to changes in sea level tidal range and wave activity but few of them describe in detail the influence of the estuarine geomorphology on the atlantic coast recent studies provide a detailed understanding of the sedimentary infill succession of incised valleys during the late holocene transgression with recent emphasis on the macrotidal bay of the vilaine river in south brittany the latter has shown the importance of the inherited morphology in controlling the preservation of the sedimentary deposits however until now there has been little information available on the geometry of the underlying bedrock of the estuary and its immediate approaches including the holocene history of the most proximal part of the vilaine river estuary the recent acquisition of very high resolution seismic reflection chirp and sediment core data in the vilaine estuary provides the opportunity to address several of these issues leading to the identification of the controlling factors that played a role in the sedimentary filling of the estuary the estuary of the vilaine river is one of the most sheltered estuaries of the atlantic coast and thus shows an excellent record of the successive transgressive phases since the last glacial period the valley of this ria type estuary is incised in the hercynian magmatic and metamorphic rocks of the armorican massif along the striking branches of the south armorican shear zone and filled with well stratified sediments the study of the morphology of the substratum in the estuary reveals narrow paleovalleys 1 km wide with a maximum depth of 20 m the shapes and dimensions of these paleovalleys are comparable with those observed upstream in the present day vilaine river valley facies analysis of seismic and sedimentary data complemented by 21 ams radiocarbon age dating enables the reconstruction of the infilling of the estuarine valley the valley is filled by pleistocene to early holocene alluvial coarse grained pebbly sands overlain by mid to late holocene marine sands silts and muds from 10 000 to 5000 cal bp the marine transgression shows a rapid initial phase of transgression followed by a progressive slowing down which can be recognised over more than 90 km in an upstream direction the rapid transgression developed homogeneously over the entire length of the estuary with a widespread expression of tidal currents tide dominated estuary the slow phase of the transgression gives rise to a differentiated expression of the hydrodynamic factors according to the geomorphological setting the sedimentary deposits of the innermost and narrow part of the estuary reflect a strong control of tidal and river currents when the influence of tidal currents increases at the expense of fluvial control in a downstream direction the sedimentary filling of the outer reaches of estuary shows a strong influence of tidal currents modulated by changes in sea level where from 5700 to 3000 cal bp the progressive decrease in accommodation space promotes the expression of wave action wave dominated estuary finally from 5000 years bp to present day the stabilisation of sea level gives birth to scour and lag sedimentary morphologies scour and lag estuary the sedimentary record appears thus strongly marked by the holocene transgression and the geomorphological setting where hydrodynamic parameters superimposed on the geomorphological and eustatic contexts expressed in different ways in time and space govern the evolution of the estuarine system

the living triserial planktic foraminifer gallitellia vivans cushman distribution stable isotopes and paleoecological implications abstract gallitellia vivans cushman is the only triserial coiling species among modern planktic foraminifera although previous studies suggested that g vivans is a planktic species it was unreported for a long time because of its small test and its low abundance in the water column and deep sea sediments therefore its distribution and ecology are poorly understood in november 2006 we collected numerous specimens of living g vivans by towed plankton net at three stations in the tsushima strait located between the east china sea and japan sea and we performed faunal assemblage and isotopic analyses g vivans were commonly observed in the water column and this species accounted for 1 4 63 1 of all living planktic foraminifera but plankton tow samples contained both living and resuspended shells stable oxygen isotopic values of g vivans ranged from 1 14 to 2 85 vpdb and indicated that their habitat is definitely planktic and that they may live at the surface on the other hand carbon isotope ratios ranged from 2 4 to 3 2 distinctly lower than values for other planktic species this may indicate isotopic disequilibrium between ambient seawater and the shells of g vivans during shell formation the geographic distribution and stable isotopic features of g vivans are shared among the multiserial planktic species that have appeared in geological history and they should also share similar ecologies and habitats the study of the ecology of g vivans is important when considering the paleoecology of primitive forms of planktic foraminifera and their surrounding environments along continental margins

oceanographic variations over the last 150 000 yr in the japan sea and synchronous holocene with the northern hemisphere abstract the paleo hydrography in the japan sea called a mini ocean was reconstructed based on the high resolution analysis of diatom assemblages over the period of 150 000 yr the decrease of diatom fertilization in the japan sea when it was isolated from surrounding seas due to the drop of sea level during the glacial to stadial phase resulted in dissolution and or extremely low diatom production in the northern cores in the subarctic water masses the annual td derived paleo ssts c were controlled by the fluctuations of 2 kyr and 4 kyr periods at intervals of 20 kyr and 40 kyr over the last 160 kyr bp respectively a 23 kyr cycle is recognized during the periods from 140 ka to 100 ka according to the wavelet analysis after temperature and sea level increased both at 133 128 ka 60 53 ka and 15 10 ka oceanic warm water diatom species predominated at 127 119 ka and after 9 cal ka in the interstadial phase at 21 3 16 9 ka and 12 9 9 8 ka sea level and salinity increased as the transgression developed at 10 0 7 0 ka the oceanic association shifted from cold water species in the stadial period to warm water ones in the interstadial phase the fluctuations of td derived ssts c on century to millennial time scales during the holocene are well correlated with abrupt climatic events that different paleoclimatic proxies record in many regions of the northern hemisphere

cyclic variation and solar forcing of holocene climate in the alaskan subarctic high resolution analyses of lake sediment from southwestern alaska reveal cyclic variations in climate and ecosystems during the holocene these variations occurred with periodicities similar to those of solar activity and appear to be coherent with time series of the cosmogenic nuclides 14c and 10be as well as north atlantic drift ice our results imply that small variations in solar irradiance induced pronounced cyclic changes in northern high latitude environments they also provide evidence that centennial scale shifts in the holocene climate were similar between the subpolar regions of the north atlantic and north pacific possibly because of sun ocean climate linkages

time dependent model of magma intrusion in and around miyake and kozu islands central japan in june august 2000 abstract a time dependent model of magma intrusion is presented for the miyake kozu island area in central japan based on global positioning system gps measurements at 28 sites recorded between june 27 and august 27 2000 a model derived from a precise hypocenter distribution map indicates the presence of three dikes between miyake and kozu islands other dike intrusion models including a dike with aseismic creep and a dike associated with a deep deflation source are also discussed the optimal parameters for each model are estimated using a genetic algorithm ga approach using akaike s information criteria aic the three dike model is shown to provide the best solution for the observed deformation volume changes in spherical inflation and deflation sources as well as three dikes are calculated for seven discretized periods after ga optimization of the dike geometry the optimization suggests a concentration of dike expansion near miyake island in the period from june 27 to july 1 associated with large deflation at a depth of about 7 km below miyake volcano indicating magma supply from depth below miyake island in the period from july 9 to august 10 a huge dike intrusion near kozu island is inferred accompanied by expansion of the lower parts of a central dike suggesting magma supply from depth in the region between miyake and kozu islands

珪藻paralia sulcataの増減からみた大陸系混合水の消長 東シナ海北東部の最終氷期 後氷期海洋環境

millennial scale holocene hydrological changes in the northeast atlantic new insights from la grande vasiere mid shelf mud belt a mid to late holocene paleohydrological reconstruction from the northeast atlantic is proposed through the study of a high resolution sedimentary record from the northern continental shelf of the

marine diatom assemblage variation across pleistocene glacial interglacial transitions from integrated ocean drilling program site c9001 northwest pacific abstract in 2006 d v chikyu cruise ck06 06 drilled hole c9001c at site c9001 in the northwest pacific ocean 80 km east of the shimokita peninsula japan an existing chronostratigraphic framework provides a continuous glacial interglacial g i climate record from which a diatom record of paleoenvironmental changes was developed across several g i cycles species counts diatom temperature values and calculated sea surface temperatures sst were produced for each sample and calibrated to prior diatom studies in this region these features were used to characterize and compare interglacial maxima of marine isotope stages mis 1 5e 9 and 11 and transitions from the preceding glacial maxima mis 9 was the longest and warmest of the four interglacials examined with a peak calculated temperature of 20 2 c maximum temperature for mis 1 of 14 9 c is only 1 c cooler than peak ssts calculated for mis 11 and 5e however the temperature trend for mis 1 continues on a linear trajectory toward warmer modern temperatures to the top of the section a lead lag relationship between sst and the benthic oxygen isotope record of ice volume was observed at the onset and reversals of major g i cycles

pliocene and pleistocene paleoceanography in the western subarctic pacific based on diatom analyses of odp leg 145 hole 884b and iodp expedition 323 holes u1341b and u1343e abstract late pliocene pleistocene fossil diatom assemblages from ocean drilling program odp leg 145 hole 884b in the western subarctic pacific were investigated to improve the diatom biostratigraphy moreover the paleoceanographic records at hole 884b were compared with those in integrated ocean drilling program iodp expedition 323 holes u1341b and u1343e in the bering sea for the time interval of 2 5 0 ma in order to clarify the differences in the diatom assemblage fluctuations and the history of past ocean circulations around the subarctic pacific in hole 884b five diatom zones from the neodenticula koizumii neodenticula kamtschatica zone to the neodenticula seminae zone were identified the decreases in the relative abundance of temperate water species were recognized at ca 1 9 ma in hole u1343e ca 2 1 ma in holes 884b and u1341b the decreases of the temperate water species at these sites indicate that a widespread cooling event must have occurred over the subarctic pacific at 2 ma in addition the continuous low occurrences of the sea ice related species from around 2 ma onward which indicate the presence of sea ice were observed at sites 884 and u1341 we also point out that the age differences in decrease of temperate water species at the three sites i e delay in response of the temperate water species at site u1343 may be related to changes of seawater inflow from the north pacific to sites u1341 and u1343 and of the east kamchatka current from the bering sea to site 884

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

diatom record of the late holocene in the okhotsk sea abstract the environmental conditions during the past 7000 cal yr bp in the okhotsk sea can be subdivided into three intervals based on diatom assemblages 1 6600 4650 cal yr bp open ocean sea ice free conditions alternated with sea ice cover 2 4650 1300 cal yr bp open ocean conditions and sea ice cover declined fluctuating with short duration and cold open ocean conditions gradually developed and 3 1300 cal yr bp present when cold open ocean conditions predominated with occasional and rapid warming chronological comparisons between climatic fluctuations and cultural history in hokkaido and okhotsk suggest that deteriorating climate could have affected local culture

seasonal variation of sediment deposition in the hudson river estuary abstract during and following the spring freshet rapid rates of sediment deposition were observed in the hudson river estuary side scan sonar surveys and sediment coring studies revealed a large amount of spatial variability in sedimentation within the estuary and a distinct seasonal progression during the freshet sediment was deposited in the seaward reaches of the estuary in the two month period after the freshet this sediment was eroded and sedimentation occurred 10 30 km further landward at the estuarine turbidity maximum etm zone the thickness of the new freshet deposit was as great as 40 cm in the etm indicating intense trapping and rapid deposition the location of this depocenter corresponded to a frontal zone where water column observations and modeling studies have indicated enhanced sediment trapping the mass of the new deposits was estimated at 300 000 metric tons during both 1998 and 1999 with similar spatial distributions in 1998 the estimated fluvial input was 560 000 metric tons significantly greater than the 120 000 metric tons estimated for 1999 thus the mass of the observed deposits appear to be more influenced by the redistribution of sediment within the estuary due to seasonal variations in erosion deposition conditions rather than by the direct input of sediment from the watershed

processes driving estuary infilling by marine sands on an embayed coast abstract detailed measurements of waves currents and sediment transport from an intertidal sandflat at the mouth of a partially filled new zealand estuary in an embayment with low littoral drift are presented with a view to establishing how marine sands are transported into the estuary waves mobilised sediments during episodic events early in events when waves were energetic sediments were in motion throughout the tidal cycle under abating waves sediment motion became intermittent finally becoming restricted to periods around low tide when wave orbital motions were able to penetrate to the bed three components of the total sediment flux were estimated from the data and analysed 1 a wind driven current which presumably has a complicated spatial expression in the vicinity of the estuary mouth controlled the net i e integrated over event direction of flux of suspended sediment entrained by waves and advected by currents there was no evidence of non symmetry over the tidal cycle in the suspension process that might drive a net sediment flux however there is some suggestion that lag in growth and decay of the estuary wave field over the tidal cycle systematically enhances offshore transport 2 net bedload transport by waves and currents was directed onshore which was guaranteed by two mechanisms firstly increasing wave orbital current skewness as the tide ebbed turned bedload transport onshore late in the ebb tide against the current and secondly bedload peaked early in the flood tide when skewed waves were reinforced by the flooding current 3 correlation between seaward directed forced mean flow and enhanced suspension under groups of high waves resulted in persistent offshore flux of suspended sediment at infragravity frequencies suspended sediment flux carried by gravity waves was directed seawards on flood tides and counter to the waves and onshore on ebb tides and with the waves which was explained in terms of a simple vortex ejection model we conclude that sediment transport on the sandflat at the mouth of this partially filled estuary is governed by subtle interactions between waves and currents that vary over the tidal cycle some interactions such as those that drive bedload transport promote estuary infilling by marine sands and others such as those that drive suspended sediment flux at infragravity frequencies do the opposite

recent evolution of the outardes estuary quebec canada consequences of dam construction on the river the outardes estuary quebec is a regressive sandy system developed in a sub boreal climatic setting the outardes river drains an area of 18 780 km2 and was dammed for hydroelectric purposes in the 1960s and 70s by reconstructing the hydrographs and mapping the morphology of the estuary from aerial photographs over a period of 21 years we have documented the changes in the estuary resulting from the modification of the hydrologic regime until the mid 1960s a catastrophic spring freshet 1800 2800 m33s 1 controlled the morphology of the estuary the mouth was dominated by a disorganized braided channel pattern and large fluvial discharge generated transverse bars peripheral channel areas in the upper estuary were zones of transport at flood stages for 18 months in 1968 and 69 the river discharge was drastically reduced 50 m3s 1 to accomplish the main reservoir filling tidal currents and waves filled and remodelled the morphology of the mouth of the estuary while the peripheral zones in the upper estuary experienced low energy sedimentation since the generating plants were brought on line in 1969 the fluvial discharge has been unable to modify substantially the sand body geometry in the mouth of the estuary in the upper estuary the peripheral regions continue to be filled in but the thalweg is being eroded based on the results of our coring programme we suggest that major environmental changes may leave a sedimentary signature addition or subtraction of size modes which can be identified by the detailed analysis of grain size distributions

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

successive oceanic and solar forcing indicated by younger dryas and early holocene climatic oscillations in the jura abstract the recent extension of 1 the residual 14 c curve back to 11 400 cal yr b p and 2 the lake level reconstruction in the jura back to ca 13 500 cal yr b p offers the opportunity of testing by proxy data the relationships between climate atmospheric 14 c the sun and the ocean recently suggested from the atmospheric 14 c record the climatic significance of the jura record is supported by correlations with climatic oscillations reconstructed in the alps from glaciers and timberline movements correspondence between the 14 c and paleoclimatic record from the jura suggests a working hypothesis two intervals within the holocene can be distinguished in the middle latitudes of western and central europe an early holocene period shows abrupt climatic oscillations linked to ocean forcing major colder climate phases developed between ca 9000 and 8800 and between ca 8000 and 7000 cal yr b c that coincide with higher 14 c values after 6000 cal yr b c a second period is characterized by smoother multicentury climatic oscillations linked to solar forcing

north pacific and north atlantic sea surface temperature variability during the holocene holocene climate variability is investigated in the north pacific and north atlantic realms using alkenone derived sea surface temperature sst records as well as a millennial scale simulation with a coupled atmosphere ocean general circulation model aogcm the alkenone sst data indicate a temperature increase over almost the entire north pacific from 7 cal kyr bp to the present a dipole pattern with a continuous cooling in the northeastern atlantic and a warming in the eastern mediterranean sea and the northern red sea is detected in the north atlantic realm similarly sst variations are opposite in sign between the northeastern pacific and the northeastern atlantic a 2300 year long aogcm climate simulation reveals a similar sst seesaw between the northeastern pacific and the northeastern atlantic on centennial time scales our analysis of the alkenone sst data and the model results suggests fundamental inter oceanic teleconnections during the holocene

paleoceanography during the last 150 kyr off central japan based on diatom floras abstract the paleoceanographic history of the area above the northern boundary of the warm kuroshio current during the last two glacial interglacial cycles was reconstructed based on high resolution records of the diatom flora in core md01 2421 ecological categories of the diatom flora were extracted using q mode factor analysis the four most prominent factors explained 91 4 of the total variance cross spectral analyses were performed on temperature estimates derived from diatom data td the relative abundance of littoral neritic diatom associations and the oxygen isotope record of benthic foraminifera diatom derived temperatures show a 50 23 and 17 kyr periodicity with only the 23 kyr band coherent with that of benthic foraminiferal oxygen isotope values littoral neritic associations show a periodicity at 62 and 17 kyr coherent with td species composition and relative abundance of the diatom flora changed at the marine isotope stage boundaries when cold water and warm water mixed over the core site due to hydrographic disturbances by changes in transport trajectory of the kuroshio current transport and global climatic changes

episodic coral growth in china s subtropical coral communities linked to broad scale climatic change evidence from the fossil coral record has shown that coral assemblages were able to extend their geographical range to higher latitudes during past global warming events in the face of future global warming scenarios we investigate the potential for china s subtropical coral communities to act as a refuge for corals as ocean temperatures continue to warm using uranium thorium dating to chronologically constrain the age of dead corals we reveal two distinct periods of coral growth between 6 85 and 5 51 ka b p and 0 11 to 0 05 ka b p relative to a d 1950 the former coincides with the mid holocene warm period when temperatures in south china were similar to 1 2 degrees c warmer than present very few ages 13 were obtained for the similar to 5 6 k y that followed an increased frequency of corals with th 230 ages dated to the past century suggests an increase in abundance coinciding with rising global temperatures nevertheless modern monitoring programs have reported a recent dramatic decline in coral cover over the past 34 yr attributable to human influences our results suggest that although coral communities existed around the subtropical islands of daya bay southeast china in the past their continued presence in the region largely depends on appropriate management of the adjacent coastline and coupled ocean atmosphere conditions similar to those experienced in the mid holocene

orbital scale anti phase variation of sea surface temperature in mid latitude north pacific margins during the last 145 000 years 1 the late quaternary records of alkenone sea surface temperature sst in the japan and california margins showed orbital scale anti phase sst variations between the two margins this east west seesaw like change agreed well with the long term el nino southern oscillation enso behavior predicted by the zebiak cane enso model clement et al 1999 as regards both the timing and frequency during 0 60 ka and 120 145 ka and is attributed to the precession controlled change in tropical enso behavior this anti phase sst change was not clearly demonstrated during 60 120 ka this finding suggests that the influence of tropical climatic dynamics on the mid latitude north pacific varied in response to glacial interglacial cycles