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

impact of the kuroshio current on the south china sea based on a 115 000 year diatom record we used the tropical oceanic planktonic diatom species nitzschia marina rhizosolenia bergonii and azpeitia africana azpeitia neocrenulata most commonly found in the surface sediments of the northeastern most south china sea scs where the kuroshio current enters the scs through the bashi strait north of luzon to analyse the influence of the the kuroshio current on the scs the impact of the kuroshio current seems to be relatively strong during major warm periods and to a lesser degree in minor warm periods during the last 115 000 years the strongest influence took place during the main part of the holocene and during the very late phase of marine isotope stage mis 5e it is possible to distinguish two magnitudes of change in the impact of the kuroshio current on the scs large changes occurred at shifts between glacial and interglacial conditions while smaller changes seem to have recurred in both glacial and interglacial episodes as well as during the holocene climatic oceanographic changes and sea level variations were possibly the two most important mechanisms for the varying influences of the kuroshio current on the scs the interaction between the kuroshio current and monsoon related processes may also have played a role however because of restricted knowledge of the present day kuroshio current and the absence of a modern analogue to the ancient scs due to the marked changes in palaeogeography this relationship is difficult to establish copyright c 2006 john wiley sons ltd less

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

holocene sea surface temperature and sea ice extent in the okhotsk and bering seas accurate prediction of future climate requires an understanding of the mechanisms of the holocene climate however the driving forces mechanisms and processes of climate change in the holocene associated with different time scales remain unclear we investigated the drivers of holocene sea surface temperature sst and sea ice extent in the north pacific ocean and the okhotsk and bering seas as inferred from sediment core records by using the alkenone unsaturation index as a biomarker of sst and abundances of sea ice related diatoms f cylindrus and f oceanica as an indicator of sea ice extent to explore controlling mechanisms in the high latitude pacific temporal changes in alkenone content suggest that alkenone production was relatively high during the middle holocene in the okhotsk sea and the western north pacific but highest in the late holocene in the eastern bering sea and the eastern north pacific the holocene variations of alkenone ssts at sites near kamchatka in the northwest pacific as well as in the western and eastern regions of the bering sea and in the eastern north pacific track the changes of holocene summer insolation at 50 n but at other sites in the western north pacific in the southern okhotsk sea and the eastern bering sea they do not in addition to insolation other atmosphere and ocean climate drivers such as sea ice distribution and changes in the position and activity of the aleutian low may have systematically influenced the timing and magnitude of warming and cooling during the holocene within the subarctic north pacific periods of high sea ice extent in both the okhotsk and bering seas may correspond to some periods of frequent or strong winter spring dust storms in the mongolian gobi desert particularly one centered at 4 3 thousand years before present kyr bp variation in storm activity in the mongolian gobi desert region may reflect changes in the strength and positions of the aleutian low and siberian high we suggest that periods of eastward displacement or increased intensity of the aleutian low correspond with times of increased extent of sea ice in the western okhotsk sea and eastern bering sea

reconstruction of surface water conditions in the central region of the okhotsk sea during the last 180 kyrs abstract core gc9a a 6 7 m long gravity core collected from the central region of the okhotsk sea during cruise yk0712 on r v yokosuka jamstec was used to reconstruct the changes in surface water conditions by measuring biogenic components biogenic opal caco3 total organic carbon and 15n of sediment organic matter of sediment samples the age of core gc9a was determined indirectly by graphic correlation comparing the b psychometric yellow blue chromaticness values with those of well dated core md01 2415 with complement to the tephra layer k3 50 ka the bottom age of core gc9a was estimated to be about 180 kyr therefore it provides the history of surface water conditions from mis 1 to mis 6 the biogenic opal caco3 and toc contents were high during the interglacial periods as expected indicating enhanced surface water production under warm climatic conditions this condition resulted from sufficient nutrient supply to the surface waters by active vertical mixing which was validated by low 15n values of the sediment organic matter in contrast surface water productivity was depressed during the colder glacial periods probably due to the expanded sea ice distribution and limited nutrient supply however the glacial sediments had moderately high 15n values indicating enhanced nitrate utilization resulting from the limited nutrient supply caused by strong stratification of the surface water high 15n values were also observed during the deglaciation which was attributed to the increased nitrate utilization during enhanced surface water productivity however the low 15n values during the glacial and deglacial periods may be attributed to the increased supply of terrestrial organic matter diatom production was primarily responsible for surface water paleoproductivity during the interglacial periods rather than coccolithophores however the succession of glacial to early deglacial coccolithophore production and late deglacial to interglacial diatom production was remarkable corresponding to the present day seasonal phytoplankton succession such an advanced coccolithophore production relative to diatom production might be attributed to the degree of nutrient availability associated with surface water conditions on the basis of variations in the 15n value finally the opal and toc contents decreased abruptly in conjunction with a gradual decrease in caco3 content from about 2 ka which seems to implicate a late holocene sudden decrease in paleoproductivity in the central region of the okhotsk sea according to the increase in 15n values during this interval nutrient availability appears to be poor which is likely attributed to the resumed strong stratification that occurred due to the southward shift of the aleutian low atmospheric pressure system

evidence of sea ice driven terrigenous detritus accumulation and deep ventilation changes in the southern okhotsk sea during the last 180 ka abstract sediment core os03 1 retrieved from the akademia nauk rise in southern okhotsk sea was analyzed for the contents of rare earth elements rees and combined with carbon isotope 13c time series of benthic foraminifera to infer changes in terrigenous accumulation and bottom water ventilation on glacial interglacial timescales in the study area the age model of os03 1 was constructed by a combination of foraminifer 18o stratigraphy and 14c ams dating revealing that the 380 cm long core provides a window on climate change in the southern okhotsk sea since 180 ka a grain size controlled ree content shows strong glacial interglacial changes the cerium and europium anomalies vary from 0 89 to 1 32 and from 1 14 to 1 37 respectively the la yb n values range between 0 55 to 0 92 both results suggest a significant contribution of volcanic debris in the core sediments in addition the relationships between sm vs nd suggest main contribution origin from the amur river and sea ice during warm intervals and from the sea ice during cold intervals indicating that the sea ice played an important role in transporting terrigenous materials to the study site in the southern okhotsk sea during the last 180 ka the mass accumulation rates mar of rees are relatively higher during glacials and lower during interglacials with a peak accumulation during the early deglacial period we infer that an intensified mongolia high is responsible for the first order accumulation pattern of rees in the southern okhotsk sea by mediating the dynamic changes in sea ice extent furthermore six 13c minima are associated with intensified asian monsoon am precipitation and maximum mars of rees indicating that the dominance of barrier layer effects by high fresh water input through sea ice melting the maximum mar of rees during the marine isotope stage mis 5c coincides with the minimum of benthic foraminiferal 13c indicating a major interruption of ventilation in the bottom water in the okhotsk sea the major low ventilation event in the deep water of the okhotsk sea appears to be dampened by a cooling condition and a major blooming of surface productivity preceded the event

formation of 26 8 26 9 σθ water in the kuril basin of the sea of okhotsk as a possible origin of north pacific intermediate water by using all japanese hydrographic data obtained south of 55 n in latitude in the sea of okhotsk we compile a data set for this study our investigations with these data show that a large quantity of relatively cold fresh oxygen rich homogeneous intermediate water with a density range of 26 8 to 26 9 exists in the kuril basin we name this intermediate water the kuril basin intermediate water kbiw results of isosteric analyses show that a possible origin of kbiw is located in a region off the hokkaido coast in the southwestern sea of okhotsk we suggest that kbiw is produced by the isopycnal mixing of relatively dense soya warm water which appears only in early spring with the colder fresher water which originates from the northwestern okhotsk finally we demonstrate that kbiw may be a source water of the north pacific intermediate water npiw because it has the same density range and water properties

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

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

a 15 000 year paleoenvironmental record from meiji seamount far northwestern pacific late glacial and holocene hemipelagic sediments from meiji seamount in the far northwest pacific contain common to abundant planktonic and benthic foraminifera for ams 14c dating for stable isotope analysis and for interpreting paleoclimate change we present here chronostratigraphic faunal and geochemical results from a piston core which indicate that during glacial times as young as 14 000 yrs bp the northwest pacific sea surface salinity was at least as low as today effectively inhibiting convective overturn between 12 000 and 13 000 yrs ago after a major flux of ice rafting there is faunal and 18o evidence of an abrupt decrease in surface ocean salinity coincident with this event was an increase in biological productivity shown by higher fluxes of calcium carbonate organic carbon opal and greater abundances and lower 13o of the benthic foraminifera uvigerina oxygen isotope ratios in uvigerina and cibicidoides show step like decreases at about 13 000 14 000 11 000 10 000 and 6000 8000 yrs bp these events may be analogous to steps in the north atlantic 18o record during meltwater events if this interpretation is correct then the temperature and salinity history of the deep pacific lags that of the north atlantic by about 1000 yrs consistent with the transport time of deep water from the north atlantic to the north pacific

a total electron content space weather study of the nighttime weddell sea anomaly of 1996 1997 southern summer with topex poseidon radar altimetry this paper reports on a total electron content space weather study of the nighttime weddell sea anomaly overlooked by previously published topex poseidon climate studies and of the nighttime ionosphere during the 1996 1997 southern summer to ascertain the morphology of spatial tec distribution over the oceans in terms of hourly geomagnetic longitudinal and summer winter variations the topex tec magnetic and published neutral wind velocity data are utilized to understand the underlying physical processes the tec results are combined with inclination and declination data plus global magnetic field line maps to investigate spatial and temporal tec variations geographic magnetic latitudes and local times are computed as results show the nighttime weddell sea anomaly is a large 1 600 2 22 million km2 estimated for a steady ionosphere space weather feature extending between 200 e and 300 e geographic it is an ionization enhancement peaking at 50 s 60 s 250 e 270 e and continuing beyond 66 s it develops where the spacing between the magnetic field lines is wide medium easterly declination is large medium 20 50 and inclination is optimum 55 s its development and hourly variations are closely correlated with wind speed variations there is a noticeable 43 reduction in its average area during the high magnetic activity period investigated southern summer nighttime tecs follow closely the variations of declination and field line configuration and therefore introduce a longitudinal division of four indian western eastern pacific atlantic northern winter nighttime tecs measured over a limited area are rather uniform longitudinally because of the small declination variation topex maps depict the expected strong asymmetry in tec distribution about the magnetic dip equator

diatoms from the surface sediments of the south china sea and their relationships to modern hydrography abstract a principal components analysis of diatoms in surface sediment samples from the south china sea scs shows a clear relationship between the spatial distributions of diatoms and the current pattern of the region six diatom assemblages are distinguished representing environments with different hydrological characteristics the neritic planktonic species thalassionema nitzschioides is the dominant component in the surface sediment diatoms with relatively small changes throughout the scs suggesting that the water mass exchanges between the scs and the pacific and indian oceans are relatively small the strongest impact of the warm oceanic water occurs in the northeasternmost part of the scs where assemblage v is located with nitzschia marina azpeitia nodulifera azpeitia neocrenulata rhizosolenia bergonii and thalassionema frauenfeldii as main taxa warm oceanic planktonic species n marina r bergonii and a neocrenulata can be used as indicators of warm oceanic waters flowing into the scs in paleoceanographic reconstructions of the area in particular in tracking the water from the western pacific including the kuroshio current it may however be problematic to use another tropical oceanic planktonic species a nodulifera as an environmental indicator because of its strong resistance to dissolution thus possibly further transport

sediment core profiles of long chain n alkanes in the sea of okhotsk enhanced transport of terrestrial organic matter from the last deglaciation to the early holocene 1 terrestrial plant derived n alkanes c25 c35 w ere measured in three piston cores pc1 pc2 and pc4 in the sea of okhotsk covering the last 30 kyrs down core profiles of the n alkane concentrations and mass accumulation rates mar were characterized by deglacial maxima in particular cores pc2 and pc4 which were collected from the central and western sea of okhotsk respectively show a two step increase around the meltwater pulse events mwp 1a 14 5 13 5 kyr bp and 1b about 10 kyr bp this finding was interpreted by the outflow of terrestrial organic matter from the submerged land shelf to the sea of okhotsk through the east sakhalin current this study demonstrated that the sea level rise forced by global warming in the deglaciation period may have caused the enhanced transport of terrestrial organic matter in marginal seas index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 1055 geochemistry organic geochemistry citation seki o k kawamura t nakatsuka k ohnishi m ikehara and m wakatsuchi sediment core profiles of long chain n alkanes in the sea of okhotsk enhanced transport of terrestrial organic matter from the last deglaciation to the early holocene geophys res lett 30 1 1001 doi 10 1029 2001gl014464 2003

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

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

last glacial maximum to holocene sea surface conditions at umnak plateau bering sea as inferred from diatom alkenone and stable isotope records 1 the bering sea gateway between the pacific and arctic oceans impacts global climate when glacial interglacial shifts in shore line position and ice coverage change regional albedo previous work has shown that during the last glacial termination and into the holocene sea level rises and sea ice coverage diminishes from perennial to absent yet existing work has not quantified sea ice duration or sea surface temperatures sst during this transition here we combine diatom assemblages with the first alkenone record from the bering sea to provide a semiquantitative record of sea ice duration sst and productivity change since the last glacial maximum lgm during the lgm diatom assemblages indicate that sea ice covered the southeastern bering sea perennially at 15 1 cal ka b p the diatom assemblage shifts to one more characteristic of seasonal sea ice and alkenones occur in the sediments in low concentrations deglaciation is characterized by laminated intervals with highly productive and diverse diatom assemblages and inferred high coccolithophorid production at 11 3 cal ka b p the diatom assemblage shifts from one dominated by sea ice species to one dominated by a warmer water north pacific species simultaneously the sst increases by 3 c and the southeastern bering sea becomes ice free year round productivity and temperature proxies are positively correlated with independently dated records from elsewhere in the bering sea the sea of okhotsk and the north pacific indicating that productivity and sst changes are coeval across the region

woce section p1w in the sea of okhotsk 1 oceanographic data description we describe the results of a world ocean circulation experiment woce survey line p1w from the open pacific ocean through the bussol strait and across the sea of okhotsk observations are presented of distributions of temperature and salinity dissolved oxygen and nutrients and some derived quantities discussion centers on the distribution of the sea of okhotsk component of the north pacific intermediate water mass and its properties the sea of okhotsk has been suggested as the only location where deep convection may occur within the north pacific or its marginal seas our analysis suggests that the surface 26 85 has recently been ventilated and arguments might be made to suggest that ventilation has occurred to 27 05 this is discussed here but detailed evidence is covered in a companion paper analyzing cfc observations the okhotsk component of the north pacific intermediate water extends to substantially greater depths and densities and so some other process is needed to create the denser water mass

water mass conversion in the glacial subarctic pacific 54 n 148 w physical constraints and the benthic planktonic stable isotope record benthic uvigerina spp cibicidoides spp gyroidinoides spp and planktonic n pachyderma sinistral g bulloides stable isotope records from three core sites in the central gulf of alaska are used to infer mixed layer and deepwater properties of the late glacial subarctic pacific glacial interglacial amplitudes of the planktonic 18o records are 1 1 1 3 less than half the amplitude observed at core sites at similar latitudes in the north atlantic these data imply that a strong negative w anomaly existed in the glacial subarctic mixed layer during the summer which points to a much stronger low salinity anomaly than exists today if true the upper water column in the north pacific would have been statically more stable than today thus suppressing convection even more efficiently this scenario is further supported by vertical i e planktic versus benthic 18o and 13c gradients of 1 which suggest that a thermohaline link between pacific deep waters and the subarctic pacific mixed layer did not exist during the late glacial epibenthic 13c in the subarctic pacific is more negative than at tropical subtropical pacific sites but similar to that recorded at southern ocean sites suggesting ventilation of the deep central pacific from mid latitude sources e g from the sea of japan and sea of okhotsk still convection to intermediate depths could have occurred in the subarctic during the winter months when heat loss to the atmosphere sea ice formation and wind driven upwelling of saline deep waters would have been most intense this would be beyond the grasp of our planktonic records which only document mixed layer temperature salinity fields extant during the warmer seasons also we do not have benthic isotope records from true intermediate water depths of the subarctic pacific

unstable holocene climate in the northeastern east sea sea of japan evidence from a diatom record abstract a total of 45 and 42 sediment subsamples from gravity cores gh98 1223 and gh98 1227 respectively were obtained in the northeastern east sea sea of japan and analyzed for diatom abundance a 14 c date for sediment organic carbon gh98 1223 along with probable and plausible correlation to the well established timeframe constrains the age to the mid to late holocene abundances of most species including neodenticulopsis seminae simonsen and kanaya simonsen and fragilariopsis doliolus wallich grunow were less than 20 in average relative to the most dominant species thalassionema nitzschioides grunow hustedt which ranged from 29 to 59 for core gh98 1223 and between 23 and 46 for core gh98 1227 frequencies of cold water species were generally higher than those of warm water species because of the high latitude cold water occupying dominantly in the basin the vertical distribution of cold water species was largely opposite to that of warm water species for example the frequency of a cold water species n seminae was inversely related to that of a warm water species f doliolus we conclude that changes in abundance of f doliolus and diatom temperature index t d value represent quasi periodic fluctuations demonstrating that the tsushima warm current and its branch of the soya warm current play a significant role in the transportation of diatom cells and heat the pulse like oscillations of this indicator species which are observed in basin wide and regional scales reflect that the strength or intensity of the dominant current is governed by a globally induced unstable climatic system during the holocene period

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

significance of the paralia sulcata fossil record in palaeoenvironmental reconstructions of the se asia marginal seas over the last glacial cycle

orbital and millennium scale environmental changes in the southern bering sea during the last glacial holocene geochemical and paleontological evidence the d 18 o benthic foraminiferal curve and ams 14 c radiocarbon data provide a representative age model for a southern bering sea sediment core gc 11 downcore profiles of d 18 oo fn pachyderma s and u auberiana carbonate and organic carbon contents species changes in the planktonic foraminifera assemblages and some diatom species show orbital mis 1 2 and 3 and millennium scale variability influenced by the alaska current flowing into the studied region three warmer episodes in the southern bering sea environment were assumed to be synchronous with do interstadials 8 12 and 14 in gisp 2 chronology during mis 3 more severe climate and environmental conditions in the southern bering sea during mis 2 occurred synchronously with the lgm within a 17 19 ka time span two well pronounced environmental warming events productivity spikes and changes in the pore water geochemistry separated by younger dryas cooling were observed at the base of mis 1 coeval with mwp 1a and 1b regional glacial primary productivity based on the calculation of the organic carbon mar similar to that found in the far northwestern pacific exceeded the late holocene values under conditions close to the present day r 2005 elsevier ltd all rights reserved

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

sediment provenance variations in the southern okhotsk sea over the last 180 ka evidence from light and heavy minerals in this study we investigate light and heavy minerals in sediment core os03 1 located at the academy of sciences rise of the southern okhotsk sea to determine their distributions and sources over the last 180 ka thousand years the sediment mainly consists of terrigenous and volcanic detritus ubiquitous drop stones and volcanic detritus throughout the core and high detrital input suggest that sea ice driven by wind and kamchatka current was the main transport agent of detrital materials to the southern okhotsk sea the ternary diagram of heavy minerals hornblende hypersthene epidote shows an expansion of detritus provenance from the eastern in cold periods to the northeastern in warm intervals of the okhotsk sea it mainly relates to the shift of aleutian low combined with previous records accumulation rates of quartz indicated a maximum extent but not perennial sea ice coverage during the glacial periods

drastic change in the late pliocene subarctic pacific diatom community associated with the onset of the northern hemisphere glaciation abstract to date there is scarcely clear understanding of the detailed responses of the subarctic pacific phytoplankton communities to the significant climate transition across the initiation of the northern hemisphere glaciation nhg approximately 2 7 million years ago we present more highly resolved evidence of the rapid and drastic change in the phytoplankton biosphere using diatom as a tracer of environmental changes and based on quantitative assemblage analysis of two marine cores from oceanic regions of the north pacific subarctic gyre in the late pliocene subarctic pacific coscinodiscus marginatus and neodenticula kamtschatica were widely dominant but the flora rapidly and drastically shifted to one rich in neodenticula complex n koizumii n seminae at the onset of nhg perhaps due to intense changes in paleoceanographic conditions such as cooling and or a collapse of the previously nutrient regime in the region we also suggest that vertical pumping of biogenic matter by diatoms may have been more efficient in this region earlier than the onset of nhg after the nhg intensification the major primary productivity role in the subarctic pacific shifted from the c marginatus rich flora to the neodenticula complex the drastic decrease of biogenic opaline accumulation reportedly associated with the initiation of nhg would have resulted from not only a decrease of primary production but also from the change in diatom assemblages and consequent effects on their principal role in export flux

palynology biostratigraphy and paleoceanography of the plio pleistocene at ocean drilling program site 887 gulf of alaska abstract analyses of marine palynomorphs including dinocysts and acritarchs from pliocene pleistocene sediments of the ocean drilling program odp site 887 in the gulf of alaska allowed the development of a biostratigraphic scheme which we compared with bio events in regional diatom and radiolarian zonations the dinocyst biostratigraphic scheme includes five biozones and four major boundaries a first stratigraphic boundary at 4 4 ma is associated with a change in productivity the other boundaries at 2 7 ma 1 7 ma and 0 7 ma correspond to the onset of the modern halocline an intensified cooling period and the end of the mid pleistocene transition respectively moreover the analyses of dinocyst assemblages illustrate long term changes in the surface ocean after 5 3 ma the occurrence of ataxiodinium zevenboomii impagidinium velorum and impagidinium patulum suggests warm temperate conditions until approximately 4 2 ma between 4 2 and 2 7 ma colder and less saline events marked by an increase in cold tolerant species such as habibacysta tectata suggest regional cooling and or lower salinity of surface water which might be related to alaskan glacier meltwater discharges from 2 7 to 1 2 ma the presence of impagidinium pallidum and cysts of pentapharsodinium dalei suggests low salinity cold and stratified surface waters whereas major drops in dinocyst fluxes are linked to a decrease in productivity and harsh conditions progressive change from cold stratified waters to warmer and saltier conditions occurred between 1 2 and 0 7 ma during the mid pleistocene transition after 0 7 ma dinocyst assemblages are characterized by the alternating dominance of brigantedinium spp and operculodinium centrocarpum suggesting fluctuations between nutrient rich low salinity cold waters and cool temperate environments

variation of alkenone sea surface temperature in the sea of okhotsk over the last 85 kyrs sea surface temperatures ssts in the sea of okhotsk were reconstructed based on alkenone unsaturation indices in two sediment cores alkenone ssts were found to range from 3 to 9 c over the last 85 kyr with higher sst values in warm periods holocene and the oxygen isotope stage ois 5a in the last glacial periods ois 4 and 3 average alkenone sst was estimated to be 4 c which was 4 c lower than the holocene on average however alkenone ssts around the last glacial maximum lgm are as high as those of the holocene the variation patterns of u k 0 37 in the okhotsk sea were found to be similar to those reported in the sea of japan org chem 32 2001 57 over the last 30 kyr although the ssts were lower in the sea of okhotsk the higher u k

decreased surface salinity in the sea of okhotsk during the last glacial period estimated from alkenones 1 studies of sediment cores from the sea of okhotsk which is characterized by seasonal sea ice have shown a large variability of sea ice indicators during the glacial interglacial cycles in this study we apply the relative abundance of the c37 4 alkenone to total c37 alkenones c37 4 as a molecular indicator of salinity and water masses to further investigate surface oceanographic condition in the sea of okhotsk in the glacial period we found a large fluctuation of c37 4 4 35 with higher values 20 35 during the last glacial period and lower values 8 during warm periods suggesting a decreased surface salinity in the glacial period the variation of c37 4 was found to be consistent with the ice rafted debris ird in the sediment core correlation coefficient r2 between c37 4 and ird 0 72 this suggests that the duration of seasonal sea ice was longer in the glacial period than today the lowered surface salinity in the glacial might also have been seriously affected by the close off of the shallow soya strait which currently transports massive volumes of saline water from the sea of japan to the sea of okhotsk

biogenic opal indicating less productive northwestern north pacific during the glacial ages 1 biogenic opal and ice rafted detritus ird data from sediments in the okhotsk sea and the neighboring north pacific revealed the remarkable reduction in opal production and southward advancement of sea ice covered area during the last glacial maximum resulting also southward shift of high biological productive area in the northwestern north pacific it implies that the substantial reduction in outflux of co2 to the atmosphere in northwestern north pacific and the pronounced increase in co2 sequestering in temperate north pacific this could be an additional co2 reduction mechanism of atmospheric co2 in the last glacial period

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

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

the new esa satellite only gravity field model via the direct approach 1 reprocessed gravity field and steady state ocean circulation explorer goce gravity gradient data were combined with data from laser geodynamics satellite lageos 1 2 and gravity recovery and climate experiment grace to generate a satellite only gravity field model to degree 260 using the direct approach named dir r4 when compared to earth gravitational model 2008 egm2008 it is more accurate at low to medium resolution thanks to goce and grace data when compared to earlier releases of esa goce models it is more accurate at high degrees owing to the larger amount of data ingested it is also slightly more accurate than esa s fourth release of the time wise model tim r4 as demonstrated by gps leveling orbit determination tests and an oceanographic evaluation according to the formal probably too optimistic by a factor of 2 2 5 cumulated geoid 1 3 cm and gravity anomaly 0 4 mgal errors at 100 km resolution the goce mission objectives have been reached

the tectonics of the okhotsk sea abstract the northern and central parts of the okhotsk sea form an epimesozoic platform the hetero aged acoustic basement is represented by deformed geosynclinal rocks from cretaceous to precambrian in age the slightly deformed sedimentary cover levelled the uneven surface of the acoustic basement and this upper paleogene neogene cover filled up the system of the structural basins the general nw se and w e extensions of the taphrogenic horsts and grabens of the acoustic basement were formed due to extension and subsidence of the earth s crust during the late paleogene neogene

characteristics of gas hydrate occurrences associated with mud diapirism and gas escape structures in the northwestern sea of okhotsk abstract an interpretation of 8450 line km of seismic reflection data acquired during four cruises in the northwestern sea of okhotsk shows widespread occurrence of free gas or gas hydrates in the sediment this occurrence is documented seismically by gas escape structures acoustic blanking and by a bottom simulating reflector bsr gas escape structures and vents are concentrated on the northern sakhalin continental margin here they are associated with local tectonic movements along a n s trending dextral shear system the inessa shear zone mud diapirism is common in the derugin basin where compression dominates this diapirism is probably closely related to the gas accumulations in the sediment below the base of the gas hydrate stability zone bghsz conductive heat flow derived from the bsr depth distribution averages about 30 8 mw m 2 only adjacent to basement highs and around the inessa shear zone do values higher than 80 22 mw m 2 occur these high values are attributed to an elevated geothermal gradient in the tectonically active zone where fluid venting takes place areas of drift sedimentation and mass wasting where sedimentation rates are high are characterised by computed heat flow values below 30 8 mw m 2 however these values must be corrected upwards by 3 20 depending on the sedimentation rate applicable 3 8 100 cm kyr the total amount of methane preserved in the hydrate stability zone hsz and trapped as free gas beneath the bsr is estimated at 17 14 10 12 m 3 for the northwestern sea of okhotsk and 15 12 10 13 m 3 for the entire sea of okhotsk the latter figure represents about 0 8 of the global reservoir of methane gas from hydrates our study documents that the semi enclosed sea of okhotsk offers favourable conditions for the accumulation of gas in its sediments on account of its subarctic climate and the prevailing hydrologic regime these conditions include high primary productivity low bottom water temperatures and high sedimentation rates

productivity and sedimentary δ15n variability for the last 17 000 years along the northern gulf of alaska continental slope 1 biogenic opal organic carbon organic matter stable isotope and trace metal data from a well dated high resolution jumbo piston core ew0408 85jc 59 33 3 n 144 9 21 w 682 m water depth recovered from the northern gulf of alaska continental slope reveal changes in productivity and nutrient utilization over the last 17 000 years maximum values of opal concentration 10 occur during the deglacial bolling allerod b a interval and earliest holocene 11 2 to 10 8 cal ka bp moderate values 6 occur during the younger dryas 13 0 to 11 2 cal ka bp and holocene and minimum values 3 5 occur during the late glacial interval lgi when converted to opal mass accumulation rates the highest values 5000 g cm 2 kyr 1 occur during the lgi prior to 16 7 cal ka bp which points to a strong influence by lgi glacimarine sedimentation regimes similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies mid holocene peaks in the terrestrial organic matter fraction at 5 5 4 7 3 5 and 1 2 cal ka bp indicate periods of enhanced delivery of glaciomarine sediments by the alaska coastal current the b a and earliest holocene intervals are laminated and enrichments of redox sensitive elements suggest dysoxic to anoxic conditions in the water column the laminations are also associated with mildly enriched sedimentary 15n ratios indicating a link between productivity nitrogen cycle dynamics and sedimentary anoxia after applying a correction for terrestrial 15n contributions based on end member mixing models of terrestrial and marine organic matter the resulting b a marine 15n 6 3 0 4 ratios are consistent with either mild denitrification or increased nitrate utilization these findings can be explained by increased micronutrient fe availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain iron input from enhanced terrestrial runoff and or the intermittent presence of seasonal sea ice resulting from altered ocean atmospheric circulation during the b a in the gulf of alaska

high resolution optically stimulated luminescence dating of a sediment core from the southwestern sea of okhotsk 1 optically stimulated luminescence osl dating is now widely accepted as a chronometer for terrestrial sediment more recently it has been suggested that osl may also be useful in the dating of deep sea marine sediments in this paper we test the usefulness of high resolution quartz osl dating in application to a 19 m marine sediment core mr0604 pc04a taken from the southwestern sea of okhotsk immediately to the north of hokkaido japan fine grained quartz 4 to 11 m was chosen as the dosimeter and a single aliquot regenerative dose protocol was used for the determination of equivalent dose de with stimulation by both infrared and blue light the suitability of the measurement procedure was confirmed using dose recovery tests a high resolution record 2 osl ages m identified clear sedimentation rate changes down the core the osl ages are significantly dependent on the water content model chosen two alternative interpretations are discussed and the geologically preferred model identified however ages resulting from the observed non modeled water content lie closest to the available radiocarbon ages in the range back to 20 ka our osl ages confirm the known high sedimentation rates in this locality and for the first time demonstrate clear differences in sedimentation rate before during and after deglaciation although the apparent accuracy of single sample ages is not always consistent with expectations average ages are accurate and our data show that osl dating can be a powerful method for establishing high resolution marine chronologies

palaeoceanography changes in the okhotsk sea during late pleistocene and holocene according to diatoms abstract paleontological records of six sediment cores in the okhotsk sea os marked the regional environmental changes over the last 140 kyr on orbital time scales the diatom assemblages and content of diatom frustules in the sediments during marine isotope stage mis 6 1 indicate the dramatic climatic and environmental changes in the os a small abundance and low diatom species diversity as well as the high percentage of near ice species indicate the cold surface environmental condition during glacial time mis 6 4 2 with low temperatures cold climate conditions and extended sea ice cover the presence of extinct redeposited species in the glacial assemblages indicates a low sea level during this time the proportion of ice species enlarged and diatom abundance reduced due to increase of the influence of the sea ice reflecting the sharp climatic cooling of adjacent land and regional environmental deterioration the subsequent increase in diatoms productivity at 129 8 117 0 kyr bp and 8 3 5 5 kyr bp indicates the strong climate warming accompanied by decrease of sea ice coverage and surface water stratification mixing of surface and intermediate water during the warmest mis in the okhotsk sea the diatom abundance and high content of the oceanic and warm water species reflect the warm surface environmental condition during mis 5e and 1 since 8 3 kyr due to decrease of the sea ice influence

geochemical and micropaleontological character of deep sea sediments from the northwestern pacific near the kuril kamchatka trench abstract sediments from the abyssal plain adjacent to the kuril kamchatka trench were collected during the german russian cruise for the kuril kamchatka biodiversity study and the chemical composition quantitative content and species composition of collected diatoms were studied the collected sediments are silt and clayey silt the sio2 am and corg contents range 7 58 19 38 and 0 44 1 55 respectively the enrichment of silts by amorphous silica indicates the presence of a significant number of organisms predominantly diatoms with an opal skeleton high corg content in sediments reflects biological productivity which is controlled by factors such as water circulation and the distribution of nutrients interrelation trends among chemical constituents is investigated via multi component statistics diatom assemblages reflect present day water masses characterized by high nutrient content surface water circulation and sedimentation conditions for different parts of the study area analysis of this new data also highlights changes in the response of diatom flora due to abiotic factors

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

paleoceanography of the gulf of alaska during the past 15 000 years results from diatoms silicoflagellates and geochemistry article i nfo abruptly during the bolling allerod bo al warm interval 14 7 12 9 cal ka declined during the younger dryas yd cold interval 12 9 to 11 7 cal kyr bp and rose again during the earliest holocene at this site the record after 11 cal kyr bp is dominated by oceanic diatoms and silicoflagellates with geochemical proxies displaying more subtle variation cores ew0408 66jc in the yakobi sea valley near cross sound and ew0408 11jc in the gulf of esquibel contain an expanded composite record along the southeast alaskan margin core 66jc contains a detailed record of the bo al and yd diatoms and silicoflagellates indicate that coastal upwelling and biosiliceous productivity were strong during the bo al but declined during the yd sea ice related diatoms increased in abundance during the yd indicating cooler but less productive waters

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

late quaternary changes of the oxygen conditions in the bottom and intermediate waters on the western kamchatka continental slope the sea of okhotsk microfossil data on the foraminifers and radiolarians in the sediment core komex lv28 44 3 the kamchatka slope in the eastern sea of okhotsk exhibit the changes in the water oxygen conditions during the last 146 ky the paleoenvironmental proxies are the radiolarian species cycladophora davisiana as indicator of the upper intermediate water ventilation and the benthic planktonic foraminifers as indicators of the bioproductivity and bottom water oxygenation in case of sediment core lv28 44 3 the bottom water represents the lower intermediate one so that conclusions on paleoenvironments are applicable for the most range of the local intermediate water the well oxygenated intermediate and near bottom waters existed in the area of study during the penultimate glaciation of mis 6 early weichselian initiation of the last glaciation within mis 5b d and last glacial stages of mis 3 2 the intervals of the short low o2 bottom events with suboxic conditions dissolved o2 in water 0 3 1 2 ml l occur during the last interglacial mis 5e eemian stage 125 to 113 ka and during the last deglaciation 17 5 to 6 5 ka eemian low o2 bottom events are associated with the high bioproductivity of the subsurface water but poor ventilation on the upper intermediate depths the low o2 bottom events during the last deglaciation occurred at the high bioproductivity of the subsurface water and active ventilation on the upper intermediate depths

millennial scale variability of holocene hydrography in the southwestern okhotsk sea diatom evidence diatom analysis of two submarine cores off eastern hokkaido island northern japan provides insights into the holocene palaeoenvironmental history of the southwestern okhotsk sea diatom flora was

late pleistocene holocene oceanographic variability in the okhotsk sea geochemical lithological and paleontological evidence sedimentary geochemical and paleontological data extracted from a sediment core taken from the central okhotsk sea record climatic and sedimentary changes over the past 100 ky benthic foraminiferal oxygen isotope record and accelerator mass spectrometry ams 14c data provide the basis for the core age chronology planktonic and benthic foraminiferal 18o and 13c measurements magnetic susceptibility ice rafted debris and coarse fraction content carbonate and organic carbon content and diatom and pollen spectra show major changes in regional climate sea surface conditions ice extent and sedimentary regime which are correlated with the global glacial interglacial changes of marine isotope stages mis 1 through 5 3 regional cooling and intensification of winter sea ice formation during the last glaciation increased the northern shelf surface water density and sea of okhotsk intermediate water soiw formation in addition to major milankovitch scale changes lithological geochemical and paleontological indices also show suborbital oscillations in okhotsk sea hydrology sedimentation and regional climate these shorter term oscillations are characterized by coupled maxima in ice rafted debris and sediment coarse fraction lithodynamic indices ldi values and most are associated with cold events involving enhanced winter ice formation and intensification of soiw and north pacific intermediate water npiw formation the terminations of ldi maxima were induced by climate warming and reductions in ice formation and were accompanied by sharp decreases in planktonic foraminiferal 18o during the glacial terminations of mis 2 and 4 however the onset of suborbital scale ldi maxima occurs close to sharp negative 18o shifts in planktonic foraminifera 18opf associated with climate warming in these special cases the ldi maxima occurred under warm climate and rising sea levels and did not lead to increases in soiw or npiw ventilation

paleoenvironmental studies of the korean peninsula inferred from diatom assemblages this paper presents a diatom history for korea and reviews some recent diatom analyses to reconstruct past environmental changes from terrestrial coastal and marine sediments around the korean peninsula since they were first reported by skvortzov in 1936 fossil diatom studies in korea have been conducted mainly from the neogene and quateranary strata of the pohang and gampo regions of gyeongsang bukdo and the chulwon and bukpyeong areas of gangwon do on the eastern coast of the korean peninsula as well as from holocene strata of the ilsan area of the han river estuary tidal sediments off mankyung dongjin namyang and hampyeong bay and the cheollipo area on the western coast of the korean peninsula most of the coastal diatoms provided further information on sea level trends climatic changes and coastal evolution for much of the holocene in the yellow sea recent studies of fossil diatoms from the ulleung basin east japan sea also indicate fluctuations in sea surface temperatures in the influx and circulation of the tsushima warm current and in sea levels during the late quaternary

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

diatoms as paleoenvironmental proxies for seasonal productivity sea ice and surface circulation in the bering sea during the late quaternary abstract diatom assemblages in suspended particulate matter spm surface sediments and piston core samples in the southern bering sea and the western subarctic pacific were examined the distribution of diatom assemblages in the southern bering sea shows not only differences in species composition between the spm and surface sediment samples but also preferential dissolution of different species in the upper water column or surface sediments furthermore we present the downcore profiles of selected diatom taxa for four piston cores to indicate changes in paleoceanographic conditions e g seasonal productivity sea ice and surface water circulation of the glacial and deglaciation periods during the late quaternary in particular we propose five models for the annual cycling of the water masses in the western subarctic pacific and the southern bering sea during the late quaternary significant regional differences in diatom accumulation rates and taxonomic composition between the southern bering sea and the western subarctic pacific reflect spatial shifts in water masses caused by the variable extent of sea ice cover and cold low salinity surface waters in these regions

sea ice conditions in the okhotsk sea during the last 550 kyr deduced from environmental magnetism 1 reconstructing past sea ice conditions in the okhotsk sea is important because sea ice conditions vary in response to global climate changes which in turn may affect global ocean circulation through intermediate water mass formation we conducted an environmental magnetic study of six cores from three stations in the central okhotsk sea to better understand temporal and spatial sea ice variations intercore correlations and age estimations are based mainly on geomagnetic paleointensity an oxygen isotope stratigraphy is available for one station magnetic susceptibility ms minima are accompanied by maxima in color b the ratio of the anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization karm sirm and the s ratio which indicates a higher proportion of biogenic to terrigenous magnetic components this reflects enhanced ocean productivity first order reversal curve diagrams and irm component analyses support the dominance of biogenic magnetite at ms minima in contrast color b karm sirm and s ratio values are low when ms is high which indicates an increased proportion of the terrigenous component that was probably transported as ice rafted debris ird for the southern two stations ird accumulation increased in glacial and deglacial periods which implies mobile sea ice conditions even in full glacials this was succeeded by extremely enhanced ocean productivity in early interglacials which suggests nearly ice free conditions for the northernmost station on the other hand ird accumulation was low in glacials and increased in early interglacials which indicates perennial sea ice coverage with little mobility in glacials succeeding ocean productivity enhancement was delayed compared to the southern stations

subarctic pacific evidence for a glacial deepening of the oceanic respired carbon pool abstract measurements of benthic foraminiferal cadmium calcium cd ca have indicated that the glacial interglacial change in deep north pacific phosphate po4 concentration was minimal which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean here we present sedimentary redox sensitive trace metal records from ocean drilling program odp site 882 nw subarctic pacific water depth 3244 m to make inferences about changes in deep north pacific oxygenation and thus respired carbon storage over the past 150 000 yr these observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment our results suggest that the deep subarctic pacific water mass was depleted in oxygen during glacial maxima though it was not anoxic we reconcile our results with the existing benthic foraminiferal cd ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed rather than remineralized this change would have corresponded to an increase in the deep pacific storage of respired carbon which would have lowered atmospheric carbon dioxide co2 by sequestering co2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea the magnitude of change in preformed nutrients suggested by the north pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pco2

extensive phytoplankton blooms in the atlantic sector of the glacial southern ocean 1 the sources and sinks of atmospheric carbon dioxide over glacial interglacial cycles are under debate variation in productivity of the antarctic circumpolar current acc could potentially play a significant role but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today we present areal and down core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire atlantic sector of the acc particularly in the seasonal ice zone siz linked to higher iron input during the last glacial sea ice acts as an effective transporter of iron and enhances its bioavailability the dominance of the deep living radiolarian cyladophora davisiana in glacial siz sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today

a biomarker approach for assessing marine and terrigenous inputs to the sediments of sea of okhotsk for the last 27 000 years abstract a sediment core taken from the sea of okhotsk which is located in the western north pacific rim with an extensive seasonal sea ice cover was investigated for lipid class compounds total organic carbon total nitrogen and 13 c of bulk organic matter to reconstruct changes in sedimentary regimes of marine and terrestrial organic matter over the last 27 kyrs higher molecular weight n alkanes fatty acids and fatty alcohols showed an increase in terrigenous inputs in glacial and to a greater extent in early deglacial periods the enhanced terrestrial input in the deglaciation stages has for the first time been found and never been reported in the open ocean biomarker profiles together with the coarse grain size distribution in nearby sediment cores suggested that sea ice rafting was the main transport mechanism of continental material to the okhotsk sea sediments however the ice rafting inputs have been weakened from 14 kyrs bp to the holocene probably due to a rapid reduction of the sea ice cover and continental shelf erosion profiles of c 37 alkenones phytol and brassicasterol as well as temporal variation in calcium carbonate and organic carbon contents indicated that the marine inputs were enhanced during the deglaciation the enhanced marine inputs were likely caused by an intensification of the primary production induced by a possibly increased nutrient supply from the continental shelves in early deglaciation and by the deglacial retreat of the sea ice cover at 14 kyrs bp this study demonstrates that biomarkers in the marginal marine sediments had recorded changes in the biogeochemical processes in the sea of okhotsk over the last 27 kyrs which may be significantly affected by changes in the okhotsk water exchange processes such as sea ice activity and sea ice transport of terrigenous materials

glacial interglacial changes in nutrient supply and stratification in the western subarctic north pacific since the penultimate glacial maximum abstract in piston cores from the open subarctic pacific and the okhotsk sea diatom bound 15n 15ndb biogenic opal calcium carbonate and barium were measured from coretop to the previous glacial maximum mis 6 glacial intervals are generally characterized by high 15ndb 8 and low productivity whereas interglacial intervals have a lower 15ndb 5 7 6 3 and indicate high biogenic productivity these data extend the regional swath of evidence for nearly complete surface nutrient utilization during glacial maxima consistent with stronger upper water column stratification throughout the subarctic region during colder intervals an early deglacial decline in 15ndb of 2 at 17 5 ka previously observed in the bering sea is found here in the open subarctic pacific record and arguably also in the okhotsk and a case can be made that a similar decrease in 15ndb occurred in both regions at the previous deglaciation as well the early deglacial 15ndb decrease best explained by a decrease in surface nutrient utilization appears synchronous with southern hemisphere associated deglacial changes and with the heinrich 1 event in the north atlantic this 15ndb decrease may signal the initial deglacial weakening in subarctic north pacific stratification and or a deglacial increase in shallow subsurface nitrate concentration if the former it would be the north pacific analogue to the increase in vertical exchange inferred for the southern ocean at the time of heinrich event 1 in either case the lack of any clear change in paleoproductivity proxies during this interval would seem to require an early deglacial decrease in the iron to nitrate ratio of subsurface nutrient supply or the predominance of light limitation of phytoplankton growth during the deglaciation prior to bolling allerod warming

okhotsk sea ice coverage and kamchatka glaciation over the last 350ka evidence from ice rafted debris and planktonic δ18o high resolution records of ice rafted debris ird and oxygen isotope records spanning an e w trending transect across the okhotsk sea unravel the marine and terrestrial cryogenic history of ne siberia over the last 350 kyr ird predominantly dispersed basin wide by sea ice shows lowest fluxes during interglacial periods implying a reduced and seasonal sea ice coverage highest ird accumulation rates are observed during glacial and deglacial periods with a more extended but highly dynamic ice cover although being rather synchronous ird fluxes are on average higher in the western okhotsk sea than in the eastern part pointing to a persistent but mobile particle supplying sea ice cover even during full glacial conditions presumably less dense in the eastern parts mis 6 is exceptional in this respect asynchronous fluxes of ird which vary spatially reflect rapid paleoclimatic and paleo glaciomarine changes ird accumulation rates were by factor 2 3 higher during mis 6 as compared to the last glacial maximum and the ird depositional center shifted from the western okhotsk sea early mis 6 toward kamchatka late mis 6 synchronous to a distinct change in the ird mineral composition both the characteristic composition of late mis 6 ird originating from the sredinny mountain range of kamchatka and their significantly enhanced accumulation rates refer to intensified iceberg dispersal across the eastern part of the okhotsk sea at 138 ka 135 ka 129 ka and 128 ka bp this scenario affords the presence of extended mountain glaciers protruding down to sea level on the western side of kamchatka anomalously light planktonic stable oxygen isotopes during mis 6 3 termination ii and mis 5 5 5 4 suggest significant freshwater supply related to the westward drainage of kamchatka glaciers the intensified kamchatka glaciation observed during late mis 6 was repeated during mis 3 iceberg discharges into the eastern okhotsk sea are observed at 60 ka 51 ka 42 ka 38 ka 36 ka and 31 ka and may partly correspond to n atlantic heinrich events

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

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

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

distribution of diatoms and geochemical features of holocene sediments from the kuril basin sea of okhotsk abstract sediments from the kuril basin were collected during the russian german deep sea expedition sokhobio sea of okhotsk biodiversity studies concentrations of biogenic and trace elements quantitative content and species composition of diatom assemblages in surface sediments and core samples were analyzed distribution in the surface sediments depending on different environmental conditions as well as changes in the diatom frustule content the ratio of dominant diatom species and the ecological structure of diatom assemblages were studied the collected sediments were silt and clayey silt with sio2am and corg contents ranging from 15 85 to 36 61 and 0 84 1 92 respectively the spatial distribution patterns of the elements studied and the diatoms as well as vertical profiles of the sediment cores revealed that the contents of biogenic components and trace elements such as amorphous silica organic carbon barium and phosphorus changed in parallel with the change in the number of diatoms and depended mainly on the biological productivity of the sea the change in water mass parameters and in the hydrological regime also affected the chemical composition of the bottom sediments over time a predominance of oceanic species is observed in the sediments at the bottom of the basin and the mixed oceanic neritic composition of diatoms is characteristic of slope deposits moreover the assemblages reflect the influence of pacific ocean water masses at stations close to the kuril straits as well as in the warm waters of the sea of japan at the station in the soya current zone a nearly synchronous increase in the impact of okhotsk water masses and the entry of the sakhalin current waters into the kuril basin as one moved deeper into the core at stations with different climatic conditions was observed the productivity and species diversity of diatoms and the chemical composition of sediments are reflections of the regional features of climatic processes

the dansgaard oeschger cycles discovered in the up stream source region of the north pacific intermediate water formation 1 millennial scale oceanographic oscillations were identified in the southern okhotsk sea based on high resolution measurements of total organic carbon toc c n ratios and biogenic opal employing core md01 2412 53 m with the bottom age of 115 ka the oscillations are linked with the dansgaard oeschger d o climatic cycles inadequate data existed in the source regions of the north pacific intermediate water npiw formation thus far we report the first decisive documentation of the d o cycles in the up stream source region of the npiw illustrating that the d o cycles observed in the down stream regions e g santa barbara basin due to expansion of the npiw were in part governed by the climatic variations occurred in the okhotsk sea increases in toc and c n ratios reflect abrupt sea level rises associated with 14 interstadial events over the past 115 kyrs attributing to the downward transport of eroded continental shelf sediments

bottom current controlled sedimentation and mass wasting in the northwestern sea of okhotsk abstract quaternary sedimentation in the northwestern sea of okhotsk where tidal and thermohaline currents are active was studied using 8443 km of high resolution air gun profiles from four cruises it is characterized by 1 bottom current controlled processes which lead to widespread deposition of contourite drifts and sediment waves on the north okhotsk continental margin and the northernmost sakhalin slope as well as to erosion and sediment reworking on the northern sakhalin shelf 2 mass wasting triggered probably by shallow earthquakes by gas hydrate instability during sea level lowstands leading to slumps and debris flows in the western derugin basin 3 deposition of the fluvial load of the river amur which results in sediment drift bodies and prograding lowstand wedges during glacial periods and to contourite drifts and a fan during interglacial times and 4 ice rafted detritus and hemipelagic sedimentation interrupted by episodic turbidity current activity especially in the derugin basin and its northern eastern and southern flanks

mid holocene sea level fluctuation inferred from diatom analysis from sediments on the west coast of korea diatoms from the ks2009 core sediment on the coast of the west sea kunsan si and the kr07 trench sediment collected from the neighboring sabsi island korea were analyzed for holocene sea level fluctuations in ks2009 core sediment results of ams 14c dating identified five stratigraphic horizons ranging from 2200 to 9100 bp the results obtained by measuring the radiocarbon dating from the kr07 were as follows 0 34 m a s l 6108 bp 0 74 m 6488 bp 1 46 m 6838 bp and 1 58 m 7208 bp diatom assemblages from ks2009 indicated facies a barren zone ks2009 23 5 to 20 3 m facies b high tidal flat ks2009 20 3 to 14 6 m holocene marine transgression facies c mid tidal flat ks2009 14 6 to 2 0 m falling sea level rising sea level facies d high tidal flat ks2009 2 to 2 m rising sea level thus after seawater influx started at 8300 bp seawater rose with fluctuations rising and falling the kr 07 trench deposit of sabsi island showed facies a barren zone kr07 1 58 to 1 18 m facies b bog kr07 1 18 to 0 76 m facies c tidal marsh kr07 0 76 to 0 52 m facies d tidal flat kr07 0 52 to 0 28 m facies e tidal marsh kr07 0 28 to 0 08 m facies f tidal flat kr07 0 08 to 0 06 m transgression occurred first about 8 300 bp at the west coast of korea around 6300 6000 bp there was a drop in the sea level and around 6000 4000 bp there was a rapid rise also repetition of falling and rising occurred since 4500 bp

magnetostratigraphy of marine sediment core md01 2414 from okhotsk sea and its paleoenvironmental implications abstract this study used a paleomagnetic method to analyze the marine sediment core called md01 2414 taken from the okhotsk sea during the images vii cruise in 2001 the results indicate that the brunhes matuyama boundary appeared at the depth of 27 76 m with the age of 0 78 ma the lower and upper bounds of the jaramillo event are located at 36 96 and 34 74 m depth respectively cobb mountain event is found at a depth between 40 67 m and 41 06 m close to the bottom of the core normal polarity is observed it is proposed to be the termination of the olduvai normal event this event implies that this core signifies an age interval of about 1 8 ma excursions could be identified from the paleomagnetic directional record such as kamikatsula santa rosa the relative paleo intensity secular variation pattern also helped to delimit magnetic excursions in the brunhes normal epoch e g iceland basin event big lost event etc thus the age model of this core can be well established based on the age model the variations of magnetic susceptibility and arm of this core indicated that highly abundant but relatively coarse grain of magnetic minerals appeared in the even stages of oxygen isotope chronology while low abundance with finer grain appeared in the interglacial periods this suggests that there are different sources and transportation pathways of the sediments deposited in the area studied during glacial and interglacial periods during the glacial time terrigenous sediments containing abundant magnetic minerals eroded by the ice river from the kamchatka peninsula were brought into the central okhotsk sea by the west kamchatkan current wkc while the central and western parts of the okhotsk sea were completely covered by sea ice during the interglacial time the wkc and the east sakhalin current esc brought lots of terrigenous sediments from the north and west the siberia continent which contain less abundant magnetic minerals and dilute the signal of magnetic susceptibility

ice rafted debris ird based sea ice expansion events during the past 100 kyrs in the okhotsk sea abstract ice rafted debris ird from sediment traps surficial sediments and sediment cores were investigated in order to reconstruct the extent history of sea ice cover during the last 100 kyrs in the okhotsk sea the seasonal ird buried into the sediments during and just after sea ice melting in spring consists of silt and sand size terrigenous particles the spatial distribution of ird within surficial sediments clearly corresponds to the extent of sea ice coverage sea ice expanded to a maximum extent during the glacial periods although sea ice cover was not perennial the okhotsk sea sea ice expansion osie events which are recognized by millennial scale abrupt peaks of ird content have occurred 13 times during the past 100 kyrs these events were amplified during the glacial periods a significant modification of the polar atmospheric circulation in the northern hemisphere is a key process in explaining these osie events

climatic and oceanological changes in the southwestern part of the sea of okhotsk during the last 94 kyr abstract this paper presents the results of a study on a sediment core obtained from the southwestern part of the sea of okhotsk by analyzing the diatoms in the sediment along with the productivity proxy and ice rafted debris data we reconstructed the regional environmental and climatic changes occurring over last 94 kyr sea ice expansion periods of active ice melting and variations in marine plankton productivity local warming and cooling events occurring in the late pleistocene and holocene periods as well as transgressive regressive fluctuations in the sea level were documented the shift in the relatively warm interglacial conditions to severe glaciation over 34 kyr ago that occurred in the studied area of the sea of okhotsk was reported for the first time the time at which the la perouse strait opened the soya current input began and the establishment of modern hydrological conditions was approximately 5 6 kyr

paleoceanographic implications of a 90 000 year long diatom record in piston core kh94 3 lm 8 off ne japan abstract q mode principal component analysis pca of a fossil diatom assemblage reveals the late quaternary paleoceanography of the nw pacific margin based on submarine core kh94 3 lm 8 recovered off the sanriku coast of ne japan 38 53 46 n 143 22 19 e overall diatoms were abundant during interglacials but low in abundance and poor in preservation during the last glacial with each oxygen isotope stage having its own characteristic assemblage the results of pca are principal component 1 pc1 is composed mainly of thalassionema nitzschioides which predominated during the coldest oxygen isotopic stages 4 75 58 ka and 2 25 11 ka and by allochthonous taxa the diatom tests are poorly preserved and the diatom mass accumulation rate dmar is the lowest in these stages pc2 is characterized by ice related diatoms that predominate in stage 3 the interstadial whereas pc3 which is characterized by neodenticula seminae and odontella aurita shows high values in stage 1 diatom assemblages exhibit drastic changes between oxygen isotopic stages 3 and 1 11 0 ka distinct increases of dmar occurred during both periods we infer an intensified advection of sea ice from the sea of okhotsk toward the area off sanriku during stage 3 this interpretation explains the high dmar in stage 3 owing to high productivity at the sea ice edge our study can contribute to marine environmental reconstruction since the last glaciation because fewer micropaleontological data exist in the nw pacific margin for these time intervals compared with other oceans

glacial to deglacial ventilation and productivity changes in the southern okhotsk sea abstract as a source region of north pacific intermediate water the okhotsk sea plays an important role in the ventilation of the north pacific to understand the detailed oceanographic changes in this marginal sea since the last glaciation we studied decadal to centennial scale proxy records from new sediment cores from the southwestern okhotsk sea glacial to holocene 14 c records of benthic foraminiferal shells suggested enhanced ventilation in the okhotsk sea during the early deglacial period between 18 and 15 ka corresponding to heinrich event 1 although the 14 c reconstruction has considerable uncertainties the okhotsk sea may have acted as a source for vigorous ventilation of the subarctic pacific during this period caco 3 preservation events appear to be better explained by the ventilation history of the okhotsk sea than by coccolithophores and foraminifera production caco 3 preservation started to improve during 18 to 15 ka and pronounced peaks in the caco 3 content corresponded to the bolling allerod 15 to 13 ka and preboreal 11 5 to 10 ka warm periods diatom and coccolithophore productivity remained low in the okhotsk sea throughout the glacial to deglacial periods different from the situation in the open subarctic pacific where high productivity was observed during the bolling allerod period after the preboreal period biogenic opal gradually increased and 15 n decreased in the southern okhotsk sea suggesting that productivity was enhanced by a relaxation of the nitrate limitation

the response of the bering sea gateway during the mid pleistocene transition abstract the mid pleistocene transition and the response of sea ice in the subarctic north pacific are examined using a diatom record from the north eastern bering sea slope iodp core u1344a high percentages of diatom sea ice species in the assemblage foster the development of groupings specific to differing ice conditions thalassiosira antarctica var borealis emerges as a key diatom species that delineates the development of thick multiannual sea ice and marks a series of advancements from 0 9 to1 2 ma after which it dominates the assemblage until 0 6 ma the decline of neodenticula seminae indicative of alaskan stream water inflow is in agreement with neighbouring core u1343e confirming the reduction of bering sea circulation after 0 9 ma we propose that during the mpt a stepped advancement of sea ice occurs in the bering sea as a response to increased moisture delivery to the high latitudes an extended period of diatom productivity between 0 75 and 0 65 ma marks major deglacial conditions towards the end of the mpt by 0 6 0 55 ma the work highlights the important role played by sea ice and supports the contention of a colder mpt in the subarctic pacific

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

controls on deglacial changes in biogenic fluxes in the north pacific ocean the subarctic north pacific ocean holds a large co2 reservoir that is currently isolated from the atmosphere by a low salinity layer it has recently been hypothesized that the reorganization of these high co2 waters may have played a crucial role in the degassing of carbon dioxide to the atmosphere during the last deglaciation this reorganization would leave some imprint on paleo productivity records here we present 230th normalized biogenic fluxes from an intermediate depth sediment core in the northwest pacific rc10 196 54 7 n 177 1 e 1007 m and place them within the context of a synthesis of previously published biogenic flux data from 49 deep sea cores north of 20 n ranging from 420 to 3968 m water depth the 230th normalized opal carbonate and organic carbon fluxes from rc10 196 peak approximately 13 000 calendar years bp during the bolling allerod b a period our data synthesis suggests that biogenic fluxes were in general lowest during the last glacial period increased somewhat in the northwest pacific during heinrich event 1 and reached a maximum across the entire north pacific during the b a period we evaluate several mechanisms as possible drivers of deglacial change in biogenic fluxes in the north pacific including changes in preservation sediment focusing sea ice extent iron inputs stratification and circulation shifts initiated in the north atlantic and north pacific our analysis suggests that while micronutrient sources likely contributed to some of the observed changes the heterogeneity in timing of glaciogenic retreat and sea level make these mechanisms unlikely causes of region wide contemporaneous peaks in export production we argue that paleoobservations are most consistent with ventilation increases in both the north pacific during h1 and north atlantic during b a being the primary drivers of increases in biogenic flux during the deglaciation as respectively they were likely to bring nutrients to the surface via increased vertical mixing and shoaling of the global thermocline

isotopic composition and morphology of living globorotalia scitula a new proxy of sub intermediate ocean carbonate chemistry abundance isotopic composition and morphological imprints of the planktonic foraminifera globorotalia scitula brady were closely examined for possible use as a novel reconstruction tool of chemical environments in sub intermediate depth seawater in the past based on the mocnes plankton tow observation of dwelling depths of g scitula and the isotopic compositions together with hydrochemistry data the empirical relations between isotopic disequilibria in carbon 13c 13cg scitula 13cdic and oxygen 18o 18og scitula 18ow isotopes in the carbonate tests and the seawater 18o and 13c of dissolved inorganic carbon dic respectively are introduced the morphological information such as pore density and porosity is also examined for significant relations to carbonate chemistry shell porosity is strongly correlated saturation state of calcite the dissolution of living g scitula tests may promote the observed isotopic differences as well as the increases in porosity 18o of g scitula is found effectively to be linear function of both water temperature and calcite saturation state and thereby temperature equation for g scitula is provided while 13c of g scitula is a linear function of only calcite saturation state the equation was validated by using globorotalia scitula collected by a sediment trap in intermediate water depths satisfactory agreements were found between observed and calculated 18o from the empirical equations based on temperature and hydrochemistry data at sediment trap deployment site indicating that the equation may be useful in paleo environmental reconstruction of sub intermediate water the sediment trap observation further suggests that the abundance of g scitula does not necessarily correspond to surface water productivity and to poc flux but instead it correlates well with the supply of fine organic matter which appears to be a result of water convection thus g scitula may be an unambiguous and excellent paleo environmental recorder for carbonate chemistry and for fine organic matter transport to the depths if isotopic and morphological observations are combined