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

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

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

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

collisional orogenesis in the northern canadian cordillera implications for cordilleran crustal structure ophiolite emplacement continental growth and the terrane hypothesis during upper triassic to lower jurassic time arc magmatic rocks of the stikine terrane arc marginal sediments of the whitehorse trough igneous and mantle rocks of the cache creek ophiolite and kutcho assemblage and oceanic sedimentary and volcanic rocks of the cache creek terrane represented a magmatic arc forearc basin forearc basement and subduction complex respectively the cache creek subduction complex was thrust to the southwest over the whitehorse trough forearc basin and the stikine terrane in the middle jurassic during collision with an inboard continental domain interpretation of the various lithotectonic assemblages of the northern intermontane belt in terms of a new plate tectonic model has a number of important implications for the canadian cordillera a the model allows comparisons to be drawn with available seismic reflection interpretations of cordilleran crustal structure b ophiolite emplacement was achieved by ramping of forearc oceanic lithosphere onto thick crustal parts of a subducting plate during collisional orogenesis c island arc collision and accretion were the principal mechanisms for continental growth with relatively minor contributions from sliced off oceanic seamounts and or plateaux and d some terrane bounding faults such as the nahlin fault do not represent major lithospheric scale boundaries and their importance in tectonic reconstructions has been overemphasised

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

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

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

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

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

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

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

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

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

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

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

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

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

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

surface wave group velocity tomography of east asia abstract group velocities of both rayleigh and love waves are used in a tomographic inversion to obtain group velocity maps of east asia 60 140 e and 20 60 n the period range studied is 30 70 s the tibetan plateau a region undergoing intense north south compression appears as a prominent low velocity about 15 from the average structure in this area central tibet appears as the area with the lowest velocities and southern tibet south of the zangbo suture zone and the himalayas is an area of high velocities the tibet low velocity area extends northward to the southern tarim basin the north china korean platform an area traditionally recognized as the oldest platform in china does not have a consistent crust and upper mantle velocity signature the north china plain a part of the platform where extensional tectonics dominates is an area of high velocities probably as a result of thin crust the other parts of the platform have relatively low velocities the south china block the least tectonically active region of china is generally an area of high velocity for periods longer than 40 s a high group velocity gradient clearly exists along longitude 105 e the velocities are noticeably higher east of this longitude than west of it this transition corresponds closely to that in the bouguer gravity map in general processes in the crust and upper mantle owing to recent tectonic activities rather than the age of the basement rocks seem to have dominant control of crust and upper mantle velocity structures

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