The study of new seismic data permits the identification of sediment gravity flows in terms of internal architecture and the distribution on shelf and abyssal setting in the Qiongdongnan Basin （QDNB）. Six gravity fl...The study of new seismic data permits the identification of sediment gravity flows in terms of internal architecture and the distribution on shelf and abyssal setting in the Qiongdongnan Basin （QDNB）. Six gravity flow types are recognized： （1） turbidite channels with a truncational basal and concordant overburden relationship along the shelf edge and slope, comprising laterally-shifting and vertically-aggrading channel complexes; （2） slides with a spoon-shaped morphology slip steps on the shelf-break and generated from the deformation of poorly-consolidated and high water content sediments; （3） slumps are limited on the shelf slope, triggered either by an anomalous slope gradient or by fault activity; （4） turbidite sheet complexes （TSC） were ascribed to the basin-floor fan and slope fan origin, occasionally feeding the deep marine deposits by turbidity currents; （5） sediment waves occurring in the lower slope-basin floor, and covering an area of approximately 400 km2, were generated beneath currents flowing across the sea bed; and （6） the central canyon in the deep water area represents an exceptive type of gravity flow composed of an association of debris flow, turbidite channels, and TSC. It presents planar multisegment and vertical multiphase characteristics. Turbidite associated with good petrophysical property in the canyon could be treated as a potential exploration target in the QDNB.展开更多
Characteristics of the pCO2 distribution in surface water of the Bering Abyssal Plain and their relationships with the ambient hydrological conditions were discussed using variations of the partial pressure of CO2 in ...Characteristics of the pCO2 distribution in surface water of the Bering Abyssal Plain and their relationships with the ambient hydrological conditions were discussed using variations of the partial pressure of CO2 in surface water of the Bering Abyssal Plain and the Chukchi Sea. Data in this study are from a field investigation during the First Chinese National Arctic Research Expedition in 1999. Compared to the high productivity in the Bering Continental Shelf, much lower levels of chlorophyll a were observed in the Bering Abyssal Plain. The effect of hydrological factors on the pCO2 distribution in surface seawater of the Plain in summer has become a major driving force and dominated over biological factors. The Plain also presents a High Nutrient Low Chlorophyll (HNLC). In addition, the pCO2 distribution in the Bering Abyssal Plain has also been found to be influenced from the Bering Slope Current which would transform to the Anadyr Cur- rent when it inflows northwestward over the Plain. The Anadyr Current would bring a high nutrient water to the western Arctic Ocean where local nutrients are almost depleted in the surface water during the summer time. Resupplying nutrients would stimulate the growth of phytoplankton and enhance capacity of absorbing atmospheric CO2 in the surface water. Otherwise, in the Bering Sea the dissolved inorganic carbon brought from freshwater are not deposited down to the deep sea water but most of them would be transported into the western Arctic Ocean by the Alaska Coastal Current to form a carbon sink there. Therefore, the two carbon sinks in the western Arctic Ocean, one carried by the Anadyr Current and another by the Alaska Costal Current, will impli- cate the western Arctic Ocean in global change.展开更多
To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is...To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is developed. Numerical computation of the annually cyclic circulation fields is performed. The results of the annual mean zonal currents and deep to abyssal western boundary currents in the equatorial Pacific Ocean are reported. The North Equatorial Current,the North Equatorial Countercurrent, the South Equatorial Current and the Equatorial Undercurrent are fairly well simulated. The model well reproduces the northward flowing abyssal western boundary current.From the model results a lower deep western boundary current east of the Bismarck-Solomon-New Hebrides Island chain at depths around 2 000 m has been found. The model results also show that the currents in the equatorial Pacific Ocean have multi-layer structures both in zonal currents and western boundary currents, indicating that the global ocean overturning thermohaline circulation appears of multi-layer pattern.展开更多
The easternmost part of Southwest Indian Ridge（SWIR） has special crustal structure, magmatic and tectonic processes. Abyssal peridotite from the easternmost part of Southwest Indian Ridge（63.5oE/28oS） is serpentin...The easternmost part of Southwest Indian Ridge（SWIR） has special crustal structure, magmatic and tectonic processes. Abyssal peridotite from the easternmost part of Southwest Indian Ridge（63.5oE/28oS） is serpentinized spinel lherzolite. The accessory spinel has zoned texture, which was studied by petrography, electron probe micro-analysis（EPMA）, and backscattered electron（BSE） imaging to reconstruct the petrotectonic and hydrothermal metamorphic history of the host abyssal peridotite. The fresh core is magmatic Al-spinel with low Cr~#. The average extent of melting of the abyssal peridotite is about 5.9%. The composition of fresh magmatic spinel core indicates the studied area to be an anomalously thin crust with a melt-poor system. Hydrothermal reaction modifies the chemical composition of magmatic spinel. Ferritchromit is the first product forming the inner rim during pre-serpentinization. The abyssal ferritchromit crystalized as micro- to nano-sized particle with no triple grain boundary, indicating they crystalized in a rapid cooling process during hydrothermal alteration. Chemical compositions of ferritchromit indicate a hydrothermal metamorphism in amphibolite facies. Magnetite in the outer rim was formed by replacement of ferritchromit during syn- or post-serpentinization. Authigenic chlorites crystallized in two events：（1） after formation of ferritchromit crystallized as vein in fracture-zone near the core of spinel and （2） after formation of magnetite crystallized at outermost rim. They are different in compositions, indicating their formation temperature was about 289 oC and declined to 214 oC. These results show that the abyssal peridotite had undergone amphibolite to lower-greenschist facies hydrothermal events during pre- to syn-serpentinization or post-serpentinization.展开更多
The mineral chemistry and texture of clinopyroxenes in peridotite from the Kingkong tectonic zone of the Southwest Indian Ridge segment in an effort to constrain mantle melting beneath this slow-spreading ridge are re...The mineral chemistry and texture of clinopyroxenes in peridotite from the Kingkong tectonic zone of the Southwest Indian Ridge segment in an effort to constrain mantle melting beneath this slow-spreading ridge are reported. There are three types of clinopyroxenes in the abyssal peridotites： coarse-grained, intergranu- lar and exsolved. The compositional variations among these three types suggest that the coarse-grained clinopyroxene is a mantle-derived source. The A1, Na and Ti contents and the Na/Ti ratio of the coarse- grained clinopyroxene may be used to monitor the degree of partial melting, combined with the contradis- tinction with Spinel Cr#, which is calculated to be between 7.9% and 14.9%, and may represent low degrees of melting in the global ocean ridge system. The along-axis compositional variations in the coarse-grained clinopyroxene suggest that the degree of partial melting is primarily controlled by the transform faults on both sides of the ridge. Nonetheless, the northwestern side of the ridge may be affected by a hypothesised detachment fault as documented by the calculated P-T conditions. Simultaneously high Na and low Ti con- tents in the coarse-grained clinoovroxene points to mantle heterogeneities along the ridge axis.展开更多
本文研究了深海钻探(DSDP)31航次296站晚新生代介形类动物群的性质及其古海洋学意义。此站钻孔上部上新统至全新统以超微浮游生物软泥和粘土为主的16块岩芯中,共分析获得介形类化石8属11种,计有:Po-seidonamicus major Benson,P.anterop...本文研究了深海钻探(DSDP)31航次296站晚新生代介形类动物群的性质及其古海洋学意义。此站钻孔上部上新统至全新统以超微浮游生物软泥和粘土为主的16块岩芯中,共分析获得介形类化石8属11种,计有:Po-seidonamicus major Benson,P.anteropunctatus Whatley et al.,P.punctatus Whatley et al.,Pennyella dorsoser-rata(Brady),Henry howella sp.,Pterygocythere mucronalatum(Brady),Abyssocythere sp.,Abyssocythereis sul-catoperforata(Brady),Pelecocythere sp.,Krithe sp.1和Krithe sp.2。这些介形类属种均为冷海域深海区介形类分子。由此表明,西北太平洋边缘地区在晚新生代曾为一深海区。在第四纪,其深度可能和现今296站的深度大致相当;在上新世,其深度可能更深一些。研究结果证实,深海底栖介形类属种的分布具全球性;在相当长的地质时期内,介形类属种的形态和壳饰都非常稳定,无明显变化。同时,进一步证实,介形类个体大小变化与深度相关,同一种介形类壳体随水域深度加深而增大。展开更多
Three volcanic ash layers were identified in a deep-sea Core IR-GC1 from the north-eastern Indian Ocean, adjacent to western Indonesian arc. They were dominated by glass shards with minor mineral crystals, such as pla...Three volcanic ash layers were identified in a deep-sea Core IR-GC1 from the north-eastern Indian Ocean, adjacent to western Indonesian arc. They were dominated by glass shards with minor mineral crystals, such as plagioclase, biotite, and hornblende. According to the morphology and major element compositions of the representative glass shards, combined with theδ18O-based age, it is suggested that ash Layer A is cor-related to the youngest Toba tuff （YTT）, Layer B is supposed to be associated with a new eruption of Toba caldera in an age of 98 to 100 ka. Ash Layer C is different the geochemistry characteristics than those of Layer A and Layer B, suggesting that Layer C was not originated from Toba but registered another volcanic erup-tion event.展开更多
Mooring observations were conducted from July 16, 2011 to March 30, 2012 east of Mindanao, Philippines （127°2.8＇E, 8°0.3＇N） to observe the abyssal current at about 5 600 m deep and 500 m above the ocean ...Mooring observations were conducted from July 16, 2011 to March 30, 2012 east of Mindanao, Philippines （127°2.8＇E, 8°0.3＇N） to observe the abyssal current at about 5 600 m deep and 500 m above the ocean bottom. Several features were revealed： 1） the observed abyssal current was highly variable with standard deviations of 57.3 mrn/s and 34.0 ram/s, larger than the mean values of-31.9 and 16.6 mm/s for the zonal and meridional components, respectively; 2） low-frequency current longer than 6 days exhibited strong seasonal variation, flowing southeastward （mean flow direction of 119.0° clockwise from north） before about October 1, 2011 and northwestward （mean flow direction of 60.5° counter-clockwise from north） thereafter; 3） the high-frequency flow bands were dominated by tidal currents O1, K1, M2, and S2, and near-inertial currents, whose frequencies were higher than the local inertial frequency. The two diurnal tidal constituents were much stronger than the two semidiumal ones. This study provides for the first time an observational insight into the abyssal western boundary current east of Mindanao based on long-term observations at one site. It is meaningful for further research into the deep and abyssal circulation over the whole Philippine Sea and the 3D structure of the westem boundary current system in this region. More observational and high-resolution model studies are needed to examine the spatial structure and temporal variation of the abyssal current over a much larger space and longer period, their relation to the upper-layer circulation, and the underlying dynamics.展开更多
ay equation migration of wide-angle reflections in 2-D medium is one kind of Kirchhoff prestack depth migration method. Based on ray theory, this method can be used extensively in 2-D inhomogeneous medium, and shows i...ay equation migration of wide-angle reflections in 2-D medium is one kind of Kirchhoff prestack depth migration method. Based on ray theory, this method can be used extensively in 2-D inhomogeneous medium, and shows its advantage in wide-angle reflection study. After calculating ray fields, we can get the wave fields of sources and receivers by interpolation, and the intensity (or amplitude) AP corresponding to the depth point P at travel-time tP=tSP+tPR can be found in seismograms. Ray equation migration is completed by transforming AP according to the specific relation, migrating it to the depth point, then calculating the ray fields of lots of sources and receivers in the same way and finally stacking the outcomes. Numerical calculation has yielded satisfactory results. Data processing of the Zhuangmu-Yuexi-Huangmei-Zhanggongdu profile passing through the Dabie orogenic zone provides a structural form of M-discontinuity along the profile. The result shows that the high pressure metamorphic rock zone of South Dabie rock mass is related to the uplifting of M-discontinuity here. 'Mountain root' exists under North Dabie rock mass, which conforms with gravity isostasy theory. The Xiaotian-Mozitan fault is a suture zone as a result of the collision of North China plate with Yangtze plate, and extends through M-discontinuity. The abyssal fault near Liu'an is the extended eastern section of the Luonan-Minggang fault, which is also confirmed here. 展开更多
Using observations in an applied cruise of the submersible Jiaolong,water characteristics,geostrophic transport,and turbulent mixing in abyssal and hadal zones of the southern Yap Trench were studied.The spatial struc...Using observations in an applied cruise of the submersible Jiaolong,water characteristics,geostrophic transport,and turbulent mixing in abyssal and hadal zones of the southern Yap Trench were studied.The spatial structures of deep water show that the abyssal water is cold,saline,and oxygen rich.The hadal water has very small changes in potential temperature and potential density,and a little decrease in salinity and obvious decrease in oxygen.The isotherm,isopycnal,and isohaline are depressed in abyss over the central trench.The turbulent mixing is enhanced in the near-bottom zone and the hadal water on the trench slope,especially at the steep slope,the dissipation rate and diffusivity is strong,which weakens the stratification.The geostrophic flows move southward in the western region of the trench and northward in the eastern region,indicating cyclonic circulation.In the central region of the trench,the water transport is^1.74 Sv southward.In the hadal zone,the northward and southward transports are balanced.Our analysis suggests that the abyssal water in the southern Yap Trench is from Lower Circumpolar Water(LCPW)and the hadal water seems to be of the isolated local water rather than LCPW.展开更多
In this paper,the intra-seasonal variability of the abyssal currents in the China Ocean Mineral Resources Association(COMRA)polymetallic nodule contact area,located in the western part of the Clarion and Clipperton Fr...In this paper,the intra-seasonal variability of the abyssal currents in the China Ocean Mineral Resources Association(COMRA)polymetallic nodule contact area,located in the western part of the Clarion and Clipperton Fraction Zone in the tropical East Pacific,is investigated using direct observations from subsurface mooring instruments as well as sea-surface height data and reanalysis products.Mooring observations were conducted from September 13,2017 to August 15,2018 in the COMRA contact area(10°N,154°W).The results were as follows:(1)At depths below 200 m,the kinetic energy of intra-seasonal variability(20-100 d)accounts for more than 40%of the overall low-frequency variability,while the ratio reaches more than 50%below 2000 m.(2)At depths below 200 m,currents show a synchronous oscillation with a characteristic time scale of 30 d,lasting from October to the following January;the energy of the 30-d oscillation increases with depth until the layer of approximately 4616 m,and the maximum velocity is approximately 10 cm/s.(3)The 30-d oscillation of deep currents is correlated with the tropical instability waves in the upper ocean.展开更多
To investigate the nature of gas hydrates in the Makran area,new high-resolution geophysical data were acquired between 2018-2019.The data collected comprise multibeam and two-dimensional multi-channel seismic reflect...To investigate the nature of gas hydrates in the Makran area,new high-resolution geophysical data were acquired between 2018-2019.The data collected comprise multibeam and two-dimensional multi-channel seismic reflection data.The multibeam bathymetry data show East-North-East(ENE)ridges,piggy-back basins,canyon and channel systems,and the morphology of the abyssal plain.Continuous and discontinuous bottom simulating reflectors(BSRs)occur in the piggy-back basins on most of the seismic profiles available.The BSRs cut the dipping layers with strong amplitude and reversed polarity.Discontinuous BSRs indicate a transition along a dipping high-permeable sand layers from gas-rich segment to the gas hydrate-bearing segment and sugge st alternating sediments of fine and relatively coarse grain size.Double BSRs are highly dynamic and attributed to slumps occurring in the study area.The BSRs induced by slumps are located both at deep and shallow depths,responding to the temperature or pressure variation.For the first time,BSRs are observed in the abyssal plain of the Makran area,being associated with anticline structures,which do not show large spatial continuity and are strongly conditioned by structural conditions such as anticlines and fluid migration pathways,including deep fault,gas chimney,and high-permeable sedimentary layer.Our results may help to assess the gas hydrate potential within the piggy-back basins and to determine the most promising target areas.Moreover,results about the abyssal plain BSR may help to locate hydrocarbon reservoirs in the deep ocean.展开更多
A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9 th Chinese Arctic Research Expedit...A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9 th Chinese Arctic Research Expedition(CHINARE-Arc9)in 2018 and previously published data.The new data reveal scours that developed at water depths of 850–1030 m with an orientation of about 75°/255°.The maximum water depth occurs in the southernmost scour and is deeper than that from previous investigations,which showed a maximum scouring depth of about 900 m on the seamount.The topographic and geomorphological characteristics suggest that these scours resulted from erosion by the ice shelf extending from the Chukchi margin and/or Laurentide Ice Sheet that grounded on the crest of the seamount and moved in a NE–SW direction.Other possibilities of their genesis include armadas of large icebergs/multi-keel icebergs calved from the Chukchi Shelf or the Laurentide Ice Sheet.The new data provide new constraints for assessing the extent and volume of the ice sheet in the Chukchi area during glacial maxima.展开更多
In this paper, the linear continuously stratified model of the abyssal circulation proposed by Pedlosky (1992) was extended to include the second order term -(γθ zzz ) in the vertical turbulent mixing parameterizati...In this paper, the linear continuously stratified model of the abyssal circulation proposed by Pedlosky (1992) was extended to include the second order term -(γθ zzz ) in the vertical turbulent mixing parameterization of - (w′θ′) z=k υθ zz -γθ zzz , in which k υ is a vertical diffusion coefficient, and γ is the second order coefficient of turbulent mixing (or simply called γ term and γ<0 is only allowed). The influence of the γ term on the baroclinic structure of the abyssal circulation driven by upwelling out of the abyss was investigated. It was found that the γ term has a noticeable influence on the baroclinic structure of the upwelling driven abyssal circulation. For uniform upwelling, it favors the baroclinic layering of the abyssal circulation in the eastern part of the basin, but prevents the layering in the west. In addition, this parameter was found to decrease the vertically averaging meridional velocity of the abyssal circulation from the west to the east on the southern boundary. For upwelling localized near the eastern boundary, the γ-term favors baroclinic layering of the abyssal circulation in the whole basin. Especially, on the southern boundary the γ-term could strengthen the vertically averaging meridional velocity in the west, but greatly weaken it in the east. The model presented here might be considered as an extension of the Pedlosky baroclinic model of the abyssal circulation.展开更多
The elpidiid holothurian Peniagone leander Pawson and Foell,1986 is recorded for the first time from the Mariana Trench area at a depth of 5571 m.The type description of this species was based on only in-situ photogra...The elpidiid holothurian Peniagone leander Pawson and Foell,1986 is recorded for the first time from the Mariana Trench area at a depth of 5571 m.The type description of this species was based on only in-situ photographs.P.leander is re-described and illustrated based on a preserved material and in-situ photographs taken on the seabed.The 16S rRNA was also obtained from the specimen and submitted to GenBank.This is the fourth discovery of this species,extending its bathymetric range in the western Pacific Ocean.展开更多
Seamounts are ubiquitous topographic units in global oceans,and their influences on local oceanic circulation have attracted great attention in physical oceanography;however,previous efforts were less made in paleocli...Seamounts are ubiquitous topographic units in global oceans,and their influences on local oceanic circulation have attracted great attention in physical oceanography;however,previous efforts were less made in paleoclimatology and paleoceanography.The Caiwei Guyot in the Magellan Seamounts of the western Pacific is a typical seamount,and in this study,we investigate a well-dated sediment core by magnetic properties to reveal the relationship between deep-sea sedimentary processes and global climate changes.The principal results are as follows:(1)the dominant magnetic minerals in the sediments are low-coercivity magnetite in pseudo-single domain range,probably including a biogenic contribution;(2)the variabilities of magnetic parameters can be clustered into two sections at~500 ka,and the differences between the two units are evident in amplitudes and means;(3)changes in the grainsize-dependent magnetic parameters can be well correlated to records of global ice volume and atmospheric CO;in the middle Pleistocene.Based on these results,a close linkage was proposed between deep-sea sedimentary processes in the Caiwei Guyot and global climate changes.This linkage likely involves different roles of biogenic magnetite in the sediments between interglacial and glacial intervals,responding to changes in marine productivity and deep-sea circulation and displaying a major change in the MidBrunhes climate event.Therefore,we proposed that the sedimentary archives at the bottom of the Caiwei Guyot record some key signals of global climate changes,providing a unique window to observe interactions between various environmental systems on glacial-interglacial timescales.展开更多
基金supported by the 973 Project(no. 2007CB411705)the National Natural Science Foundations of China(no.40806019)+1 种基金the Key Laboratory of Marginal Sea Geology,Chinese Academy of Sciences (no.MSGL09-10)the Key Laboratory of Tectonics and Petroleum Resources(China University of Geosciences)project(no.TPR-2009-17)
文摘The study of new seismic data permits the identification of sediment gravity flows in terms of internal architecture and the distribution on shelf and abyssal setting in the Qiongdongnan Basin （QDNB）. Six gravity flow types are recognized： （1） turbidite channels with a truncational basal and concordant overburden relationship along the shelf edge and slope, comprising laterally-shifting and vertically-aggrading channel complexes; （2） slides with a spoon-shaped morphology slip steps on the shelf-break and generated from the deformation of poorly-consolidated and high water content sediments; （3） slumps are limited on the shelf slope, triggered either by an anomalous slope gradient or by fault activity; （4） turbidite sheet complexes （TSC） were ascribed to the basin-floor fan and slope fan origin, occasionally feeding the deep marine deposits by turbidity currents; （5） sediment waves occurring in the lower slope-basin floor, and covering an area of approximately 400 km2, were generated beneath currents flowing across the sea bed; and （6） the central canyon in the deep water area represents an exceptive type of gravity flow composed of an association of debris flow, turbidite channels, and TSC. It presents planar multisegment and vertical multiphase characteristics. Turbidite associated with good petrophysical property in the canyon could be treated as a potential exploration target in the QDNB.
基金supported by the National Natural Science Foundation of China(Grant No.40276001).
文摘Characteristics of the pCO2 distribution in surface water of the Bering Abyssal Plain and their relationships with the ambient hydrological conditions were discussed using variations of the partial pressure of CO2 in surface water of the Bering Abyssal Plain and the Chukchi Sea. Data in this study are from a field investigation during the First Chinese National Arctic Research Expedition in 1999. Compared to the high productivity in the Bering Continental Shelf, much lower levels of chlorophyll a were observed in the Bering Abyssal Plain. The effect of hydrological factors on the pCO2 distribution in surface seawater of the Plain in summer has become a major driving force and dominated over biological factors. The Plain also presents a High Nutrient Low Chlorophyll (HNLC). In addition, the pCO2 distribution in the Bering Abyssal Plain has also been found to be influenced from the Bering Slope Current which would transform to the Anadyr Cur- rent when it inflows northwestward over the Plain. The Anadyr Current would bring a high nutrient water to the western Arctic Ocean where local nutrients are almost depleted in the surface water during the summer time. Resupplying nutrients would stimulate the growth of phytoplankton and enhance capacity of absorbing atmospheric CO2 in the surface water. Otherwise, in the Bering Sea the dissolved inorganic carbon brought from freshwater are not deposited down to the deep sea water but most of them would be transported into the western Arctic Ocean by the Alaska Coastal Current to form a carbon sink there. Therefore, the two carbon sinks in the western Arctic Ocean, one carried by the Anadyr Current and another by the Alaska Costal Current, will impli- cate the western Arctic Ocean in global change.
基金This study is supported by the National Natural Sci-ence Foundation of China under contract No.40136010the Major State Basic Research Program of China under contract No.G1999043808the Youth Fund of National“863”Project of China under contract No.2002AA639350.
文摘To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is developed. Numerical computation of the annually cyclic circulation fields is performed. The results of the annual mean zonal currents and deep to abyssal western boundary currents in the equatorial Pacific Ocean are reported. The North Equatorial Current,the North Equatorial Countercurrent, the South Equatorial Current and the Equatorial Undercurrent are fairly well simulated. The model well reproduces the northward flowing abyssal western boundary current.From the model results a lower deep western boundary current east of the Bismarck-Solomon-New Hebrides Island chain at depths around 2 000 m has been found. The model results also show that the currents in the equatorial Pacific Ocean have multi-layer structures both in zonal currents and western boundary currents, indicating that the global ocean overturning thermohaline circulation appears of multi-layer pattern.
基金supported by the National Natural Science Foundation of China (No. 41172050)the Special Fund for Basic Scientific Research of Central Universities, China University of Geosciences (Wuhan)the China Postdoctoral Science Foundation
文摘The easternmost part of Southwest Indian Ridge（SWIR） has special crustal structure, magmatic and tectonic processes. Abyssal peridotite from the easternmost part of Southwest Indian Ridge（63.5oE/28oS） is serpentinized spinel lherzolite. The accessory spinel has zoned texture, which was studied by petrography, electron probe micro-analysis（EPMA）, and backscattered electron（BSE） imaging to reconstruct the petrotectonic and hydrothermal metamorphic history of the host abyssal peridotite. The fresh core is magmatic Al-spinel with low Cr~#. The average extent of melting of the abyssal peridotite is about 5.9%. The composition of fresh magmatic spinel core indicates the studied area to be an anomalously thin crust with a melt-poor system. Hydrothermal reaction modifies the chemical composition of magmatic spinel. Ferritchromit is the first product forming the inner rim during pre-serpentinization. The abyssal ferritchromit crystalized as micro- to nano-sized particle with no triple grain boundary, indicating they crystalized in a rapid cooling process during hydrothermal alteration. Chemical compositions of ferritchromit indicate a hydrothermal metamorphism in amphibolite facies. Magnetite in the outer rim was formed by replacement of ferritchromit during syn- or post-serpentinization. Authigenic chlorites crystallized in two events：（1） after formation of ferritchromit crystallized as vein in fracture-zone near the core of spinel and （2） after formation of magnetite crystallized at outermost rim. They are different in compositions, indicating their formation temperature was about 289 oC and declined to 214 oC. These results show that the abyssal peridotite had undergone amphibolite to lower-greenschist facies hydrothermal events during pre- to syn-serpentinization or post-serpentinization.
基金The National Basic Research Program of China under contract No.2013CB429705the Public Science and Technology Research Funds Projects of Ocean,the State Oceanic Administration of the People's Republic of China under contract No.201005003+1 种基金the National Natural Science Foundation of China under contract Nos 41106051,40906037 and 41176045the Fundamental Research Funds of the State Oceanic Administration of the People's Republic of China under contract No.JT1001
文摘The mineral chemistry and texture of clinopyroxenes in peridotite from the Kingkong tectonic zone of the Southwest Indian Ridge segment in an effort to constrain mantle melting beneath this slow-spreading ridge are reported. There are three types of clinopyroxenes in the abyssal peridotites： coarse-grained, intergranu- lar and exsolved. The compositional variations among these three types suggest that the coarse-grained clinopyroxene is a mantle-derived source. The A1, Na and Ti contents and the Na/Ti ratio of the coarse- grained clinopyroxene may be used to monitor the degree of partial melting, combined with the contradis- tinction with Spinel Cr#, which is calculated to be between 7.9% and 14.9%, and may represent low degrees of melting in the global ocean ridge system. The along-axis compositional variations in the coarse-grained clinopyroxene suggest that the degree of partial melting is primarily controlled by the transform faults on both sides of the ridge. Nonetheless, the northwestern side of the ridge may be affected by a hypothesised detachment fault as documented by the calculated P-T conditions. Simultaneously high Na and low Ti con- tents in the coarse-grained clinoovroxene points to mantle heterogeneities along the ridge axis.
基金The National Natural Science Foundation of China under contract Nos 41106052 91228101 and 41306056the Fundamental Research Funds for National Nonprofit Institute Grant under contract No.JG0910
文摘Three volcanic ash layers were identified in a deep-sea Core IR-GC1 from the north-eastern Indian Ocean, adjacent to western Indonesian arc. They were dominated by glass shards with minor mineral crystals, such as plagioclase, biotite, and hornblende. According to the morphology and major element compositions of the representative glass shards, combined with theδ18O-based age, it is suggested that ash Layer A is cor-related to the youngest Toba tuff （YTT）, Layer B is supposed to be associated with a new eruption of Toba caldera in an age of 98 to 100 ka. Ash Layer C is different the geochemistry characteristics than those of Layer A and Layer B, suggesting that Layer C was not originated from Toba but registered another volcanic erup-tion event.
基金Supported by the China Postdoctoral Science Foundation(No.2013M530331)the Project of State Strategic Program of Global Change(No.2013CB956202)
文摘Mooring observations were conducted from July 16, 2011 to March 30, 2012 east of Mindanao, Philippines （127°2.8＇E, 8°0.3＇N） to observe the abyssal current at about 5 600 m deep and 500 m above the ocean bottom. Several features were revealed： 1） the observed abyssal current was highly variable with standard deviations of 57.3 mrn/s and 34.0 ram/s, larger than the mean values of-31.9 and 16.6 mm/s for the zonal and meridional components, respectively; 2） low-frequency current longer than 6 days exhibited strong seasonal variation, flowing southeastward （mean flow direction of 119.0° clockwise from north） before about October 1, 2011 and northwestward （mean flow direction of 60.5° counter-clockwise from north） thereafter; 3） the high-frequency flow bands were dominated by tidal currents O1, K1, M2, and S2, and near-inertial currents, whose frequencies were higher than the local inertial frequency. The two diurnal tidal constituents were much stronger than the two semidiumal ones. This study provides for the first time an observational insight into the abyssal western boundary current east of Mindanao based on long-term observations at one site. It is meaningful for further research into the deep and abyssal circulation over the whole Philippine Sea and the 3D structure of the westem boundary current system in this region. More observational and high-resolution model studies are needed to examine the spatial structure and temporal variation of the abyssal current over a much larger space and longer period, their relation to the upper-layer circulation, and the underlying dynamics.
文摘ay equation migration of wide-angle reflections in 2-D medium is one kind of Kirchhoff prestack depth migration method. Based on ray theory, this method can be used extensively in 2-D inhomogeneous medium, and shows its advantage in wide-angle reflection study. After calculating ray fields, we can get the wave fields of sources and receivers by interpolation, and the intensity (or amplitude) AP corresponding to the depth point P at travel-time tP=tSP+tPR can be found in seismograms. Ray equation migration is completed by transforming AP according to the specific relation, migrating it to the depth point, then calculating the ray fields of lots of sources and receivers in the same way and finally stacking the outcomes. Numerical calculation has yielded satisfactory results. Data processing of the Zhuangmu-Yuexi-Huangmei-Zhanggongdu profile passing through the Dabie orogenic zone provides a structural form of M-discontinuity along the profile. The result shows that the high pressure metamorphic rock zone of South Dabie rock mass is related to the uplifting of M-discontinuity here. 'Mountain root' exists under North Dabie rock mass, which conforms with gravity isostasy theory. The Xiaotian-Mozitan fault is a suture zone as a result of the collision of North China plate with Yangtze plate, and extends through M-discontinuity. The abyssal fault near Liu'an is the extended eastern section of the Luonan-Minggang fault, which is also confirmed here.
基金Supported by the National Key Basic Research Program of China(973 Program)(No.2015CB755904)the National Natural Science Foundation of China(No.41276036)。
文摘Using observations in an applied cruise of the submersible Jiaolong,water characteristics,geostrophic transport,and turbulent mixing in abyssal and hadal zones of the southern Yap Trench were studied.The spatial structures of deep water show that the abyssal water is cold,saline,and oxygen rich.The hadal water has very small changes in potential temperature and potential density,and a little decrease in salinity and obvious decrease in oxygen.The isotherm,isopycnal,and isohaline are depressed in abyss over the central trench.The turbulent mixing is enhanced in the near-bottom zone and the hadal water on the trench slope,especially at the steep slope,the dissipation rate and diffusivity is strong,which weakens the stratification.The geostrophic flows move southward in the western region of the trench and northward in the eastern region,indicating cyclonic circulation.In the central region of the trench,the water transport is^1.74 Sv southward.In the hadal zone,the northward and southward transports are balanced.Our analysis suggests that the abyssal water in the southern Yap Trench is from Lower Circumpolar Water(LCPW)and the hadal water seems to be of the isolated local water rather than LCPW.
基金The Fund of China Ocean Mineral Resources R&D Association under contract No.DY135-E2-5-01the National Program on Global Change and Air-Sea InteractionⅡunder contract No.GASI-04-WLHY-01。
文摘In this paper,the intra-seasonal variability of the abyssal currents in the China Ocean Mineral Resources Association(COMRA)polymetallic nodule contact area,located in the western part of the Clarion and Clipperton Fraction Zone in the tropical East Pacific,is investigated using direct observations from subsurface mooring instruments as well as sea-surface height data and reanalysis products.Mooring observations were conducted from September 13,2017 to August 15,2018 in the COMRA contact area(10°N,154°W).The results were as follows:(1)At depths below 200 m,the kinetic energy of intra-seasonal variability(20-100 d)accounts for more than 40%of the overall low-frequency variability,while the ratio reaches more than 50%below 2000 m.(2)At depths below 200 m,currents show a synchronous oscillation with a characteristic time scale of 30 d,lasting from October to the following January;the energy of the 30-d oscillation increases with depth until the layer of approximately 4616 m,and the maximum velocity is approximately 10 cm/s.(3)The 30-d oscillation of deep currents is correlated with the tropical instability waves in the upper ocean.
基金the Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology(No.MMRKF201810)the China Geological Survey(Nos.DD20190582,DD20191009,DD20160214)funded by the Shandong Province"Taishan Scholar"Construction Project。
文摘To investigate the nature of gas hydrates in the Makran area,new high-resolution geophysical data were acquired between 2018-2019.The data collected comprise multibeam and two-dimensional multi-channel seismic reflection data.The multibeam bathymetry data show East-North-East(ENE)ridges,piggy-back basins,canyon and channel systems,and the morphology of the abyssal plain.Continuous and discontinuous bottom simulating reflectors(BSRs)occur in the piggy-back basins on most of the seismic profiles available.The BSRs cut the dipping layers with strong amplitude and reversed polarity.Discontinuous BSRs indicate a transition along a dipping high-permeable sand layers from gas-rich segment to the gas hydrate-bearing segment and sugge st alternating sediments of fine and relatively coarse grain size.Double BSRs are highly dynamic and attributed to slumps occurring in the study area.The BSRs induced by slumps are located both at deep and shallow depths,responding to the temperature or pressure variation.For the first time,BSRs are observed in the abyssal plain of the Makran area,being associated with anticline structures,which do not show large spatial continuity and are strongly conditioned by structural conditions such as anticlines and fluid migration pathways,including deep fault,gas chimney,and high-permeable sedimentary layer.Our results may help to assess the gas hydrate potential within the piggy-back basins and to determine the most promising target areas.Moreover,results about the abyssal plain BSR may help to locate hydrocarbon reservoirs in the deep ocean.
基金The National Natural Science Foundation of China under contract No.41976079the Chinese Polar Environment Comprehensive Investigation and Assessment Programmes under contract No.CHINARE-03-03。
文摘A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9 th Chinese Arctic Research Expedition(CHINARE-Arc9)in 2018 and previously published data.The new data reveal scours that developed at water depths of 850–1030 m with an orientation of about 75°/255°.The maximum water depth occurs in the southernmost scour and is deeper than that from previous investigations,which showed a maximum scouring depth of about 900 m on the seamount.The topographic and geomorphological characteristics suggest that these scours resulted from erosion by the ice shelf extending from the Chukchi margin and/or Laurentide Ice Sheet that grounded on the crest of the seamount and moved in a NE–SW direction.Other possibilities of their genesis include armadas of large icebergs/multi-keel icebergs calved from the Chukchi Shelf or the Laurentide Ice Sheet.The new data provide new constraints for assessing the extent and volume of the ice sheet in the Chukchi area during glacial maxima.
文摘In this paper, the linear continuously stratified model of the abyssal circulation proposed by Pedlosky (1992) was extended to include the second order term -(γθ zzz ) in the vertical turbulent mixing parameterization of - (w′θ′) z=k υθ zz -γθ zzz , in which k υ is a vertical diffusion coefficient, and γ is the second order coefficient of turbulent mixing (or simply called γ term and γ<0 is only allowed). The influence of the γ term on the baroclinic structure of the abyssal circulation driven by upwelling out of the abyss was investigated. It was found that the γ term has a noticeable influence on the baroclinic structure of the upwelling driven abyssal circulation. For uniform upwelling, it favors the baroclinic layering of the abyssal circulation in the eastern part of the basin, but prevents the layering in the west. In addition, this parameter was found to decrease the vertically averaging meridional velocity of the abyssal circulation from the west to the east on the southern boundary. For upwelling localized near the eastern boundary, the γ-term favors baroclinic layering of the abyssal circulation in the whole basin. Especially, on the southern boundary the γ-term could strengthen the vertically averaging meridional velocity in the west, but greatly weaken it in the east. The model presented here might be considered as an extension of the Pedlosky baroclinic model of the abyssal circulation.
基金the National Key R&D Program of China(No.2018YFC0309804)the China Ocean Mineral Resources Research and Development Association Program(No.DY135-E2-3-04)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB42000000)the Biological Resources Program,Chinese Academy of Sciences(No.KFJ-BRP-017-38)。
文摘The elpidiid holothurian Peniagone leander Pawson and Foell,1986 is recorded for the first time from the Mariana Trench area at a depth of 5571 m.The type description of this species was based on only in-situ photographs.P.leander is re-described and illustrated based on a preserved material and in-situ photographs taken on the seabed.The 16S rRNA was also obtained from the specimen and submitted to GenBank.This is the fourth discovery of this species,extending its bathymetric range in the western Pacific Ocean.
基金The Natural Science Foundation of Shanghai under contract No.19ZR1459800the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract No.GML2019ZD0106the Project of Global Changing and Air-sea Interaction under contract No.GASI-GEOGE-04
文摘Seamounts are ubiquitous topographic units in global oceans,and their influences on local oceanic circulation have attracted great attention in physical oceanography;however,previous efforts were less made in paleoclimatology and paleoceanography.The Caiwei Guyot in the Magellan Seamounts of the western Pacific is a typical seamount,and in this study,we investigate a well-dated sediment core by magnetic properties to reveal the relationship between deep-sea sedimentary processes and global climate changes.The principal results are as follows:(1)the dominant magnetic minerals in the sediments are low-coercivity magnetite in pseudo-single domain range,probably including a biogenic contribution;(2)the variabilities of magnetic parameters can be clustered into two sections at~500 ka,and the differences between the two units are evident in amplitudes and means;(3)changes in the grainsize-dependent magnetic parameters can be well correlated to records of global ice volume and atmospheric CO;in the middle Pleistocene.Based on these results,a close linkage was proposed between deep-sea sedimentary processes in the Caiwei Guyot and global climate changes.This linkage likely involves different roles of biogenic magnetite in the sediments between interglacial and glacial intervals,responding to changes in marine productivity and deep-sea circulation and displaying a major change in the MidBrunhes climate event.Therefore,we proposed that the sedimentary archives at the bottom of the Caiwei Guyot record some key signals of global climate changes,providing a unique window to observe interactions between various environmental systems on glacial-interglacial timescales.
