This study examines the relationship between the subtropical high in the West Pacific and the Okhotsk high in summer, and explains why the subtropical high cannot progress northward when the Okhotsk high is active. Th...This study examines the relationship between the subtropical high in the West Pacific and the Okhotsk high in summer, and explains why the subtropical high cannot progress northward when the Okhotsk high is active. The findings are as follows. (1) A teleconnection pattern, namely, the significant correlation dipole between the index of the Okhotsk high and 500 hPa geopotential height (Z500), over East Asia, tends to occur in summer. (2) The teleconnection is closely related to the wave train propagation from the Okhotsk Sea via Japan to the subtropical regions when the Okhotsk high is developing. (3) The wave train propagation associated with the development of the Okhotsk high can generate a large cyclonic anomaly over the sea east of Japan, even in late summer. The cyclonic anomaly plays an important role in weakening the northern part of the subtropical high. The anomalous southern position of the main body of the subtropical high in the summer of 1998 is partly due to this effect.展开更多
A large amount of igneous rocks in NE China formed in an extensional setting during Late Mesozoic. However, there is still controversy about how the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean effected the lithos...A large amount of igneous rocks in NE China formed in an extensional setting during Late Mesozoic. However, there is still controversy about how the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean effected the lithosphere in NE China. In this paper, we carried out a comprehensive study for andesites from the Keyihe area using LA-ICP-MS zircon UPb dating and geochemical and Hf isotopic analysis to investigate the petrogenesis and tectonic setting of these andesites. The U-Pb dating yields an Early Cretaceous crystallization age of 128.3±0.4 Ma. Geochemically, the andesites contain high Sr(686-930 ppm) and HREE contents, low Y(11.9-19.8 ppm) and Yb(1.08-1.52 ppm) contents, and they therefore have high Sr/Y(42-63) and La/Yb(24-36) ratios, showing the characteristics of adakitic rocks. Moreover, they exhibit high K2O/Na2O ratios(0.57-0.81), low Mg O contents(0.77-3.06 wt%), low Mg# value(17-49) and negative εHf(t) values(-1.7 to-8.5) with no negative Eu anomalies, indicating that they are not related to the oceanic plate subduction. Based on the geochemical and isotopic data provided in this paper and regional geological data, it can be concluded that the Keyihe adakitic rocks were affected by the Mongol-Okhotsk tectonic regime, forming in a transition setting from crustal thickening to regional extension thinning. They were derived from the partial melting of the thickened lower crust. The closure of the Mongol-Okhotsk Ocean may finish in early Early Cretaceous, followed by the collisional orogenic process. The southern part region of its suture belt was in a post-orogenic extensional setting in the late Early Cretaceous.展开更多
Based on field investigation in 1999, two deformational domains with d ifferent dynamics have been distinguished from the Jurassic geological outcrops in the Mohe area of NE China, i.e. northern ductile and southern p...Based on field investigation in 1999, two deformational domains with d ifferent dynamics have been distinguished from the Jurassic geological outcrops in the Mohe area of NE China, i.e. northern ductile and southern plastic-brittl e ones. Their deformational features are stated in this paper. And then, three st ages of structural deformation of the area relative to the late Mesozoic orogeni c processes of Mongolian-Okhotsk orogen are reconstructed as follows, (1) south w ards thrusting in the middle-late Jurassic, (2) eastwards thrusting and strike -s lipping parallel to the orogen in the late Jurassic, and (3) southeastwards thru sting in the early Cretaceous.展开更多
The Mesozoic geodynamic evolution of Transbaikalia has been largely controlled by the scissors-like closure of the Mongol-Okhotsk Ocean that separated Siberia from Mongolia-North China continents.Following the oceanic...The Mesozoic geodynamic evolution of Transbaikalia has been largely controlled by the scissors-like closure of the Mongol-Okhotsk Ocean that separated Siberia from Mongolia-North China continents.Following the oceanic closure,the tectonic evolution of that region was characterized by collisional uplift and subsequent extension that gave rise to the formation of metamorphic core complexes.This complex tectonic setting prevailed simultaneously between 150 Ma and 110 Ma both in Transbaikalia,North Mongolia,and within the North China Craton.Published paleobotanical and paleontological data show that the oldest Mesozoic basins had formed in western Transbaikalia before the estimated age of extension onset.However no precise geochronological age is available for the onset of extension in Transbaikalia.The Tugnuy Basin,as probably the oldest Mesozoic basin in western Transbaikalia,is a key obj ect to date the onset of extension and following changes in tectonic setting.In this study,U-Pb(LA-ICP-MS)dating of detrital zircons from three key Jurassic sediment formations of the Tugnuy Basin are used to identify the potential source areas of the sediments,understand the changes in sediment routing and provide insights on the topographic evolution of western Transbaikalia.Our results show several significant changes in tectonic regime after the closure of the Mongol-Okhotsk Ocean.A wide uplifted plateau formed during the closure of the Mongol-Okhotsk Ocean,determining the Early Jurassic drainage system reaching the AngaraVitim batholith to the north and shedding sediments to the continental margin to the South.The following collisional event at the end of the Early Jurassic led to the uplift of the collision zone,which partially inverted the drainage system toward the North.A strike-slip displacement induced by the oblique collision initiated some of the early Transbaikalian depressions,such as the Tugnuy Basin at about 168 Ma.A phase of basin inversion,marked by folding and erosion of the Upper Jurassic sediments,could correspond to the short-term collision event that took place during the latest Jurassic-earliest Cretaceous in the eastern Central Asian Orogenic Belt.The following inversion in tectonic regime from compression to extension is consistent with the mid-lower-crustal extension that led to the formation of the numerous metamorphic core complexes throughout northeastern continental Asia during the Early Cretaceous.展开更多
80 sediment stations and 4 sediment cores collected in the Sea of Okhotsk were used in this study in order to reveal additional proxy for past climate reconstruction based on planktonic foraminifera. Variation in dive...80 sediment stations and 4 sediment cores collected in the Sea of Okhotsk were used in this study in order to reveal additional proxy for past climate reconstruction based on planktonic foraminifera. Variation in diversity indices (Simpson, Shannon and equitability indices) along the sea became additional criteria for 5 biogeographical provinces based on planktonic foraminifera. All of them show different structure aspects of the planktonic foraminifera assemblages that is very informative in cases of high relative abundance of N. pachyderma sin. and influence of carbonate dissolution factor. During the last 100 ky the diversity indices were changed and we can assume the migration of biogeographical provinces borders: borders of the Northern province were mov- ed to the central part in cold MIS 2, 4, structure of assemblages during MIS 3, 5 was close to the modern Central province but characterized by low total foraminiferal abundance in the sediments. The Simpson and Shannon indices are more sensitive to changes in structure of planktonic foraminifera assemblages when equitability index varies lightly during the Late Pleistocene-Holocene.展开更多
The given investigation presents the results of estimating the water circulation in the water area of the Bering Sea and the Sea of Okhotsks, considering the influence of various types of the atmospheric processes. To...The given investigation presents the results of estimating the water circulation in the water area of the Bering Sea and the Sea of Okhotsks, considering the influence of various types of the atmospheric processes. To solve the given problem it is used a hydrodynamic model calculating the integral functions of the flow from the surface to the bottom. By results of calculations, the maps of the integral water circulation were built for the following types of atmospheric circulation： ＂north-western＂ and ＂okhotsk-aleutian＂. In accordance with the performed calculations for the water area being studied, the hydrodynamic structures are distinguished both non-depending and depending on the type of the atmospheric circulation. The non-depending structures are characterized by the cyclonic activity in the Bering Sea and the Sea of Okhotsk in whole. Hydrodynamic structures depending on types of the atmospheric circulation have their peculiarities in the spatial-temporal distribution.展开更多
The research works of methane concentration in water column of the Okhotsk Sea from 1984 to 2005 were reviewed.And some regularities of methane distribution in water column in the North-East Sakhalin slope of the Okho...The research works of methane concentration in water column of the Okhotsk Sea from 1984 to 2005 were reviewed.And some regularities of methane distribution in water column in the North-East Sakhalin slope of the Okhotsk Sea were concluded.展开更多
Based on the analysis of known geodynamic models that explain the processes in various geodynamic settings of the Meso-Cenozoic stages of the development of continental margins and the tectonic-magmatic events accompa...Based on the analysis of known geodynamic models that explain the processes in various geodynamic settings of the Meso-Cenozoic stages of the development of continental margins and the tectonic-magmatic events accompanying these processes, as well as on the basis of our own data obtained as a result of many years of research on the axial structure of the Central Asian Fold Belt-Mongol-Okhotsk orogenic belt and the influence of interdependent structures on the post-Mesozoic evolution of the eastern flank of the Mongol-Okhotsk orogenic belt was substantiated by us. The closure of the Mongol-Okhotsk basin due to the approach of the Siberian and North China cratons was accompanied by a change in geodynamic conditions: subduction, collision, intraplate-rift and was reflected in the formation of synchronous igneous complexes in the frame of the Mongol-Okhotsk orogenic belt. In the northern frame of the belt, the distribution of magmatites is cut off by the structure of the Selenga-Stanovoy superterrane in the west. The northern boundary of the superterrane is the zone of the Dzheltulak fault. In the south, it borders on the Mongol-Okhotsk orogenic belt along the zone of tectonic melange. We believe that evolutionary processes within the orogenic belt and its framing continued into the post-Mesozoic time after the final formation of the belt as an orogen. The position of the Selenga-Stanovoy superterrane in the late Mesozoic did not correspond to the modern one. The structures of the Central Asian fold belt located between the Mongol-Okhotsk orogenic belt and the Siberian craton in the Cenozoic were influenced by collisional processes occurring between the Indian and Eurasian plates. And these processes were not only the “driving force” for the movement of the Selenga-Stanovoy superterrane in the post-Mesozoic time, but also changed the structure of the Mongol-Okhotsk orogen, dividing it into two flanks.展开更多
The following geochemical types of granitoids have been investigated in the Mongol-Okhotsk belt:tholetitic,palingenic calc-alkaline,latitic,plumasitic and arpaitic rare-metal granites.Plagiogranites of the tholeiitic ...The following geochemical types of granitoids have been investigated in the Mongol-Okhotsk belt:tholetitic,palingenic calc-alkaline,latitic,plumasitic and arpaitic rare-metal granites.Plagiogranites of the tholeiitic series occur within the Mongol-Okhotsk suture,indicating a subduction environment.The calc-alkaline granitoids responsible for the batholith-like intrusions and their formation are related to collision environments.The latest granitoids of the latite series and rare-metal granites came into existence after the collision of continental masses,providing evidence of intraplate magmatism.展开更多
Multidisciplinary field investigations were carried out in Okhotsk Sea by R/V Akademik M.A. Lavrentyev (LV) of the Russian Academy of Sciences (RAS) in May 2006, supported by funding agencies from Ko- rea, Russia, Jap...Multidisciplinary field investigations were carried out in Okhotsk Sea by R/V Akademik M.A. Lavrentyev (LV) of the Russian Academy of Sciences (RAS) in May 2006, supported by funding agencies from Ko- rea, Russia, Japan and China. Geophysical data including echo-sounder, bottom profile, side-scan- sonar, and gravity core sample were obtained aimed to understand the characteristics and formation mechanism of shallow gas hydrates. Based on the geophysical data, we found that the methane flare detected by echo-sounder was the evidence of free gas in the sediment, while the dome structure de- tected by side-scan sonar and bottom profile was the root of gas venting. Gas hydrate retrieved from core on top of the dome structure which was interbedded as thin lamination or lenses with thickness varying from a few millimeters to 3 cm. Gas hydrate content in hydrate-bearing intervals visually amounted to 5%―30% of the sediment volume. This paper argued that gases in the sediment core were not all from gas hydrate decomposition during the gravity core lifting process, free gases must existed in the gas hydrate stability zone, and tectonic structure like dome structure in this paper was free gas central, gas hydrate formed only when gases over-saturated in this gas central, away from these struc- tures, gas hydrate could not form due to low gas concentration.展开更多
The existence of discontinuities, the topographies of the 410 km and 660 km discontinuities, and the penetrations of subducting slabs near the 660 km discontinuities beneath the Sea of Okhotsk were studied using Nth r...The existence of discontinuities, the topographies of the 410 km and 660 km discontinuities, and the penetrations of subducting slabs near the 660 km discontinuities beneath the Sea of Okhotsk were studied using Nth root slant stack and digital records from networks in Germany and the western United States. Results show the obvious evidence for reflected and refractive phases associated with the 410 km and 660 km discontinuities. There may be discontinuities at other depths such as 150 km, 220 km and 520 km. The 410 km discontinuity is elevated and the 660 km discontinuity is depressed respectively, consistent with the expected thermal signature of the phase transitions. The subducting slab has penetrated into the lower mantle in the northern part of the Sea of Okhotsk, while it is stagnant on the 660 km discontinuity in the southern part.展开更多
The study examined effects of sea surface temperature anomalies （SSTAs） off the east coast of Japan on the blocking high over the Okhotsk Sea in June by diagnostic analysis and numerical simulation. Firstly, based o...The study examined effects of sea surface temperature anomalies （SSTAs） off the east coast of Japan on the blocking high over the Okhotsk Sea in June by diagnostic analysis and numerical simulation. Firstly, based on 500-hPa geopotential height fields, the Okhotsk high index （OKHI） for June from 1951 to 2000 is calculated and analyzed. The result indicates that the OKHI has obvious inter-annual and inter-decadal vaxiations, and there are 9 yr of high OKHI and 8 yr of low OKHI in 50 yr. Secondly, by using the OKHI, the relationship between the Okhotsk high and the 500-hPa geopotential height anomaly is investigated. The results indicate that the ＂＋-＋＂ pattern of geopotential height anomaly crossing Eurasia in the mid-high latitudes and the ＂＋-＂ pattern of geopotential height anomaly from high to low latitudes over East Asia are in favor of the formation and maintenance of the Okhotsk high. The relationship between the OKHI and the SSTA over the North Pacific is investigated in early summer by using correlation and composite analysis. We found that when the blocking circulation over the Okhotsk Sea occurs, there is an obvious negative SSTA off the east coast of Japan in early summer. We simulated the effects of the negative SSTA of east coast of Japan on the atmospheric circulation anomaly over East Asia through the control and sensitivity experiments using NCAR CAM3 model in order to confirm our analysis results. The simulation shows that the negative SSTA off the east coast of Japan results in the significant positive 40 gpm 500-hPa geopotential height anomaly over the Okhotsk Sea and the negative anomalies off the east coast of Japan which might contribute to the formation and development of the Okhotsk high in June.展开更多
基金This study was supported by the National Natural Science Foundation of China under Grant No. 49794030 and the Ministry of Science Technology of China (G1998040908).
文摘This study examines the relationship between the subtropical high in the West Pacific and the Okhotsk high in summer, and explains why the subtropical high cannot progress northward when the Okhotsk high is active. The findings are as follows. (1) A teleconnection pattern, namely, the significant correlation dipole between the index of the Okhotsk high and 500 hPa geopotential height (Z500), over East Asia, tends to occur in summer. (2) The teleconnection is closely related to the wave train propagation from the Okhotsk Sea via Japan to the subtropical regions when the Okhotsk high is developing. (3) The wave train propagation associated with the development of the Okhotsk high can generate a large cyclonic anomaly over the sea east of Japan, even in late summer. The cyclonic anomaly plays an important role in weakening the northern part of the subtropical high. The anomalous southern position of the main body of the subtropical high in the summer of 1998 is partly due to this effect.
基金supported by the National Natural Science Foundation of China (Grant No. 41872234 and 41340024)Self-determined Foundation of Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources (Grant No. DBYZZ-18-08)Graduate Innovation Fund of Jilin University
文摘A large amount of igneous rocks in NE China formed in an extensional setting during Late Mesozoic. However, there is still controversy about how the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean effected the lithosphere in NE China. In this paper, we carried out a comprehensive study for andesites from the Keyihe area using LA-ICP-MS zircon UPb dating and geochemical and Hf isotopic analysis to investigate the petrogenesis and tectonic setting of these andesites. The U-Pb dating yields an Early Cretaceous crystallization age of 128.3±0.4 Ma. Geochemically, the andesites contain high Sr(686-930 ppm) and HREE contents, low Y(11.9-19.8 ppm) and Yb(1.08-1.52 ppm) contents, and they therefore have high Sr/Y(42-63) and La/Yb(24-36) ratios, showing the characteristics of adakitic rocks. Moreover, they exhibit high K2O/Na2O ratios(0.57-0.81), low Mg O contents(0.77-3.06 wt%), low Mg# value(17-49) and negative εHf(t) values(-1.7 to-8.5) with no negative Eu anomalies, indicating that they are not related to the oceanic plate subduction. Based on the geochemical and isotopic data provided in this paper and regional geological data, it can be concluded that the Keyihe adakitic rocks were affected by the Mongol-Okhotsk tectonic regime, forming in a transition setting from crustal thickening to regional extension thinning. They were derived from the partial melting of the thickened lower crust. The closure of the Mongol-Okhotsk Ocean may finish in early Early Cretaceous, followed by the collisional orogenic process. The southern part region of its suture belt was in a post-orogenic extensional setting in the late Early Cretaceous.
文摘Based on field investigation in 1999, two deformational domains with d ifferent dynamics have been distinguished from the Jurassic geological outcrops in the Mohe area of NE China, i.e. northern ductile and southern plastic-brittl e ones. Their deformational features are stated in this paper. And then, three st ages of structural deformation of the area relative to the late Mesozoic orogeni c processes of Mongolian-Okhotsk orogen are reconstructed as follows, (1) south w ards thrusting in the middle-late Jurassic, (2) eastwards thrusting and strike -s lipping parallel to the orogen in the late Jurassic, and (3) southeastwards thru sting in the early Cretaceous.
基金supported by grants from the Russian Foundation for Basic Research(Grant No.17-05-00191)joint programme of Russian Foundation for Basic Research,Russia(No.13-05-91052)CNRS,France(PICS 4881)。
文摘The Mesozoic geodynamic evolution of Transbaikalia has been largely controlled by the scissors-like closure of the Mongol-Okhotsk Ocean that separated Siberia from Mongolia-North China continents.Following the oceanic closure,the tectonic evolution of that region was characterized by collisional uplift and subsequent extension that gave rise to the formation of metamorphic core complexes.This complex tectonic setting prevailed simultaneously between 150 Ma and 110 Ma both in Transbaikalia,North Mongolia,and within the North China Craton.Published paleobotanical and paleontological data show that the oldest Mesozoic basins had formed in western Transbaikalia before the estimated age of extension onset.However no precise geochronological age is available for the onset of extension in Transbaikalia.The Tugnuy Basin,as probably the oldest Mesozoic basin in western Transbaikalia,is a key obj ect to date the onset of extension and following changes in tectonic setting.In this study,U-Pb(LA-ICP-MS)dating of detrital zircons from three key Jurassic sediment formations of the Tugnuy Basin are used to identify the potential source areas of the sediments,understand the changes in sediment routing and provide insights on the topographic evolution of western Transbaikalia.Our results show several significant changes in tectonic regime after the closure of the Mongol-Okhotsk Ocean.A wide uplifted plateau formed during the closure of the Mongol-Okhotsk Ocean,determining the Early Jurassic drainage system reaching the AngaraVitim batholith to the north and shedding sediments to the continental margin to the South.The following collisional event at the end of the Early Jurassic led to the uplift of the collision zone,which partially inverted the drainage system toward the North.A strike-slip displacement induced by the oblique collision initiated some of the early Transbaikalian depressions,such as the Tugnuy Basin at about 168 Ma.A phase of basin inversion,marked by folding and erosion of the Upper Jurassic sediments,could correspond to the short-term collision event that took place during the latest Jurassic-earliest Cretaceous in the eastern Central Asian Orogenic Belt.The following inversion in tectonic regime from compression to extension is consistent with the mid-lower-crustal extension that led to the formation of the numerous metamorphic core complexes throughout northeastern continental Asia during the Early Cretaceous.
文摘80 sediment stations and 4 sediment cores collected in the Sea of Okhotsk were used in this study in order to reveal additional proxy for past climate reconstruction based on planktonic foraminifera. Variation in diversity indices (Simpson, Shannon and equitability indices) along the sea became additional criteria for 5 biogeographical provinces based on planktonic foraminifera. All of them show different structure aspects of the planktonic foraminifera assemblages that is very informative in cases of high relative abundance of N. pachyderma sin. and influence of carbonate dissolution factor. During the last 100 ky the diversity indices were changed and we can assume the migration of biogeographical provinces borders: borders of the Northern province were mov- ed to the central part in cold MIS 2, 4, structure of assemblages during MIS 3, 5 was close to the modern Central province but characterized by low total foraminiferal abundance in the sediments. The Simpson and Shannon indices are more sensitive to changes in structure of planktonic foraminifera assemblages when equitability index varies lightly during the Late Pleistocene-Holocene.
文摘The given investigation presents the results of estimating the water circulation in the water area of the Bering Sea and the Sea of Okhotsks, considering the influence of various types of the atmospheric processes. To solve the given problem it is used a hydrodynamic model calculating the integral functions of the flow from the surface to the bottom. By results of calculations, the maps of the integral water circulation were built for the following types of atmospheric circulation： ＂north-western＂ and ＂okhotsk-aleutian＂. In accordance with the performed calculations for the water area being studied, the hydrodynamic structures are distinguished both non-depending and depending on the type of the atmospheric circulation. The non-depending structures are characterized by the cyclonic activity in the Bering Sea and the Sea of Okhotsk in whole. Hydrodynamic structures depending on types of the atmospheric circulation have their peculiarities in the spatial-temporal distribution.
文摘The research works of methane concentration in water column of the Okhotsk Sea from 1984 to 2005 were reviewed.And some regularities of methane distribution in water column in the North-East Sakhalin slope of the Okhotsk Sea were concluded.
文摘Based on the analysis of known geodynamic models that explain the processes in various geodynamic settings of the Meso-Cenozoic stages of the development of continental margins and the tectonic-magmatic events accompanying these processes, as well as on the basis of our own data obtained as a result of many years of research on the axial structure of the Central Asian Fold Belt-Mongol-Okhotsk orogenic belt and the influence of interdependent structures on the post-Mesozoic evolution of the eastern flank of the Mongol-Okhotsk orogenic belt was substantiated by us. The closure of the Mongol-Okhotsk basin due to the approach of the Siberian and North China cratons was accompanied by a change in geodynamic conditions: subduction, collision, intraplate-rift and was reflected in the formation of synchronous igneous complexes in the frame of the Mongol-Okhotsk orogenic belt. In the northern frame of the belt, the distribution of magmatites is cut off by the structure of the Selenga-Stanovoy superterrane in the west. The northern boundary of the superterrane is the zone of the Dzheltulak fault. In the south, it borders on the Mongol-Okhotsk orogenic belt along the zone of tectonic melange. We believe that evolutionary processes within the orogenic belt and its framing continued into the post-Mesozoic time after the final formation of the belt as an orogen. The position of the Selenga-Stanovoy superterrane in the late Mesozoic did not correspond to the modern one. The structures of the Central Asian fold belt located between the Mongol-Okhotsk orogenic belt and the Siberian craton in the Cenozoic were influenced by collisional processes occurring between the Indian and Eurasian plates. And these processes were not only the “driving force” for the movement of the Selenga-Stanovoy superterrane in the post-Mesozoic time, but also changed the structure of the Mongol-Okhotsk orogen, dividing it into two flanks.
文摘The following geochemical types of granitoids have been investigated in the Mongol-Okhotsk belt:tholetitic,palingenic calc-alkaline,latitic,plumasitic and arpaitic rare-metal granites.Plagiogranites of the tholeiitic series occur within the Mongol-Okhotsk suture,indicating a subduction environment.The calc-alkaline granitoids responsible for the batholith-like intrusions and their formation are related to collision environments.The latest granitoids of the latite series and rare-metal granites came into existence after the collision of continental masses,providing evidence of intraplate magmatism.
基金Korean MOMAF Program (Grant No. PM06020)Key Discipline Program of Chinese Academy of Sciences (Grant No. KZCX2-211-01)+1 种基金High Tech-nology Research and Development Program of China (Grant No. 2006AA09Z234)National Natural Science Foundation of China (Grant No. 40776032)
文摘Multidisciplinary field investigations were carried out in Okhotsk Sea by R/V Akademik M.A. Lavrentyev (LV) of the Russian Academy of Sciences (RAS) in May 2006, supported by funding agencies from Ko- rea, Russia, Japan and China. Geophysical data including echo-sounder, bottom profile, side-scan- sonar, and gravity core sample were obtained aimed to understand the characteristics and formation mechanism of shallow gas hydrates. Based on the geophysical data, we found that the methane flare detected by echo-sounder was the evidence of free gas in the sediment, while the dome structure de- tected by side-scan sonar and bottom profile was the root of gas venting. Gas hydrate retrieved from core on top of the dome structure which was interbedded as thin lamination or lenses with thickness varying from a few millimeters to 3 cm. Gas hydrate content in hydrate-bearing intervals visually amounted to 5%―30% of the sediment volume. This paper argued that gases in the sediment core were not all from gas hydrate decomposition during the gravity core lifting process, free gases must existed in the gas hydrate stability zone, and tectonic structure like dome structure in this paper was free gas central, gas hydrate formed only when gases over-saturated in this gas central, away from these struc- tures, gas hydrate could not form due to low gas concentration.
基金This work was supported by the Special Funds for the State Major Basic Research of China (Grant No. 95-13-04-06)the National Natural Science Foundation of China (Grant No. 49874020)the Ph.D. Programs Foundation of the Ministry of Education of Chi
文摘The existence of discontinuities, the topographies of the 410 km and 660 km discontinuities, and the penetrations of subducting slabs near the 660 km discontinuities beneath the Sea of Okhotsk were studied using Nth root slant stack and digital records from networks in Germany and the western United States. Results show the obvious evidence for reflected and refractive phases associated with the 410 km and 660 km discontinuities. There may be discontinuities at other depths such as 150 km, 220 km and 520 km. The 410 km discontinuity is elevated and the 660 km discontinuity is depressed respectively, consistent with the expected thermal signature of the phase transitions. The subducting slab has penetrated into the lower mantle in the northern part of the Sea of Okhotsk, while it is stagnant on the 660 km discontinuity in the southern part.
基金the Major State Basic Research & Development Program under No. 2004CB418300 from the Ministry of Science and Technology of Chinathe NSFC Key Project under No. 40675034the Sino-Japan Research Center for Meteorological Disaster, the JICA project.
文摘The study examined effects of sea surface temperature anomalies （SSTAs） off the east coast of Japan on the blocking high over the Okhotsk Sea in June by diagnostic analysis and numerical simulation. Firstly, based on 500-hPa geopotential height fields, the Okhotsk high index （OKHI） for June from 1951 to 2000 is calculated and analyzed. The result indicates that the OKHI has obvious inter-annual and inter-decadal vaxiations, and there are 9 yr of high OKHI and 8 yr of low OKHI in 50 yr. Secondly, by using the OKHI, the relationship between the Okhotsk high and the 500-hPa geopotential height anomaly is investigated. The results indicate that the ＂＋-＋＂ pattern of geopotential height anomaly crossing Eurasia in the mid-high latitudes and the ＂＋-＂ pattern of geopotential height anomaly from high to low latitudes over East Asia are in favor of the formation and maintenance of the Okhotsk high. The relationship between the OKHI and the SSTA over the North Pacific is investigated in early summer by using correlation and composite analysis. We found that when the blocking circulation over the Okhotsk Sea occurs, there is an obvious negative SSTA off the east coast of Japan in early summer. We simulated the effects of the negative SSTA of east coast of Japan on the atmospheric circulation anomaly over East Asia through the control and sensitivity experiments using NCAR CAM3 model in order to confirm our analysis results. The simulation shows that the negative SSTA off the east coast of Japan results in the significant positive 40 gpm 500-hPa geopotential height anomaly over the Okhotsk Sea and the negative anomalies off the east coast of Japan which might contribute to the formation and development of the Okhotsk high in June.
