The existing estimates of the volume transport from the Pacific Ocean to the South China Sea are summarized, showing an annual mean westward transport, with the Taiwan Strait outflow subtracted, of 3.5±2.0 Sv （1...The existing estimates of the volume transport from the Pacific Ocean to the South China Sea are summarized, showing an annual mean westward transport, with the Taiwan Strait outflow subtracted, of 3.5±2.0 Sv （1 Sv=-0^6 ma s^-1）. Results of a global ocean circulation model show an annual mean transport of 3.9 Sv from the Pacific to the Indian Ocean through the South China Sea. The boreal winter transport is larger and exhibits a South China Sea branch of the Pacific-to-Indian Ocean throughflow, which originates from the western Philippine Sea toward the Indonesian Seas through the South China Sea, as well as through the Karimata and Mindoro Straits. The southwestward current near the continental slope of the northern South China Sea is shown to be a combination of this branch and the interior circulation gyre. This winter branch can be confirmed by trajectories of satellite-tracked drifters, which clearly show a flow from the Luzon Strait to the Karimata Strait in winter. In summer, the flow in the Karimata Strait is reversed. Numerical model results indicate that the Pacific water can enter the South China Sea and exit toward the Sulu Sea, but no observational evidence is available. The roles of the throughiiow branch in the circulation, water properties and air-sea exchange of the South China Sea, and in enhancing and regulating the volume transport and reducing the heat transport of the Indonesian Throughflow, are discussed.展开更多
Ecological systems in the headwaters of the Yellow River, characterized by hash natural environmental conditions, are very vulnerable to climatic change. In the most recent decades, this area greatly attracted the pub...Ecological systems in the headwaters of the Yellow River, characterized by hash natural environmental conditions, are very vulnerable to climatic change. In the most recent decades, this area greatly attracted the public's attention for its more and more deteriorating environmental conditions. Based on tree-ring samples from the Xiqing Mountain and A'nyêmagên Mountains at the headwaters of the Yellow River in the Northeastern Tibetan Plateau, we reconstructed the minimum temperatures in the winter half year over the last 425 years and the maximum temperatures in the summer half year over the past 700 years in this region. The variation of minimum temperature in the winter half year during the time span of 1578―1940 was a relatively stable trend, which was followed by an abrupt warming trend since 1941. However, there is no significant warming trend for the maximum temperature in the summer half year over the 20th century. The asymmetric variation patterns between the minimum and maximum temperatures were observed in this study over the past 425 years. During the past 425 years, there are similar variation patterns between the minimum and maximum temperatures; however, the minimum temperatures vary about 25 years earlier compared to the maximum temperatures. If such a trend of variation patterns between the minimum and maximum temperatures over the past 425 years continues in the future 30 years, the maximum temperature in this region will increase significantly.展开更多
A dipole structure anomaly in summer Arctic atmospheric variability is identified in this study, which is characterized by the second mode of empirical orthogonal function (EOF) analysis of summer monthly mean sea lev...A dipole structure anomaly in summer Arctic atmospheric variability is identified in this study, which is characterized by the second mode of empirical orthogonal function (EOF) analysis of summer monthly mean sea level pressure (SLP) north of 70°N, accounting for 12.94% of the variance. The dipole anom- aly shows a quasi-barotropic structure with opposite anomalous centers over the Canadian Arctic and the Beaufort Sea and between the Kara Sea and the Laptev Sea. The dipole anomaly reflects alternating variations in location of the polar vortex between the western and eastern Arctic regions. The positive phase of the dipole anomaly corresponds to the center of the polar vortex over the western Arctic, leading to an increase in summer mean rainfall in Northeast China. The dipole anomaly has a pre- dominant 6-year periodicity, and shows interdecadal variations in recent decades.展开更多
Rapid declines in Arctic sea ice have captured attention and pose significant challenges to a variety of stakeholders. There is a rising demand for Arctic sea ice prediction at daily to seasonal time scales, which is ...Rapid declines in Arctic sea ice have captured attention and pose significant challenges to a variety of stakeholders. There is a rising demand for Arctic sea ice prediction at daily to seasonal time scales, which is partly a sea ice initial condition problem. Thus, a multivariate data assimilation that integrates sea ice observations to generate realistic and skillful model initialization is needed to improve predictive skill of Arctic sea ice. Sea ice data assimilation is a relatively new research area. In this review paper, we focus on two challenges for implementing multivariate data assimilation systems for sea ice forecast. First, to address the challenge of limited spatiotemporal coverage and large uncertainties of observations, we discuss sea ice parameters derived from satellite remote sensing that(1) have been utilized for improved model initialization, including concentration, thickness and drift, and(2) are currently under development with the potential for enhancing the predictability of Arctic sea ice, including melt ponds and sea ice leads. Second, to strive to generate the ‘‘best" estimate of sea ice initial conditions by combining model simulations/forecasts and observations, we review capabilities and limitations of different data assimilation techniques that have been developed and used to assimilate observed sea ice parameters in dynamical models.展开更多
Recent tree-ring studies in Mongolia provide evidence of unusual warming that is in agreement with large-scale reconstructed and recorded temperatures for the Northern Hemisphere and the Arctic. One Mongolian proxy re...Recent tree-ring studies in Mongolia provide evidence of unusual warming that is in agreement with large-scale reconstructed and recorded temperatures for the Northern Hemisphere and the Arctic. One Mongolian proxy record for temperature extends back over 1000 years and several others are over 350 years in length. Precipitation reconstructions based on tree rings reflect recent increases but also indicate that the increases are within the long-term range of variations. Spectral analyses of recorded precipitation data and the reconstructions support the hypotheses of quasi-solar periodicity in precipitation variation, previously suggested by others.展开更多
In order to quantitatively estimate the volume and property transports between the South China Sea and Indonesian Seas via the Karimata Strait, two trawi-resistant bottom mounts, with ADCPs embedded, were deployed in ...In order to quantitatively estimate the volume and property transports between the South China Sea and Indonesian Seas via the Karimata Strait, two trawi-resistant bottom mounts, with ADCPs embedded, were deployed in the strait to measure the velocity profile as part of the South China Sea-Indonesian Seas trans- port/exchange （SITE） program. A pair of surface and bottom acoustic modems was employed to transfer the measured velocity without recovering the mooring. The advantage and problems of the instruments in this field work are reported and discussed. The field observations confirm the existence of the South Chi- na Sea branch of Indonesian throughflow via the Karimata Strait with a stronger southward flow in boreal winter and weaker southward bottom flow in boreal summer, beneath the upper layer northward （reversal） flow. The estimate of the averaged volume, heat and freshwater transports from December 2007 to March 2008 （winter） is （-2.7±1.1）×10^6 m^3/s, （-0.30±0.11） PW, 2008 （summer） is （1.2±0.6）×10^6 m^3/s, （0.14±0.03） PW, （-0.18±0.07） × 106 m3/s and from May to September （0.12±0.04）×10^6 m^3/s and for the entire record from December 2007 to October 2008 is （-0.5±1.9）×10^6 m^3/s, （-0.05±0.22） PW, （-0.01±0.15）×10^6 m^3/s （nega- tive/positive represents southward/northward transport）, respectively. The existence of southward bottom flow in boreal summer implies that the downward sea surface slope from north to south as found by Fang et al. （2010） for winter is a year-round phenomenon.展开更多
The first near continuous mollusk fossil record from the Qinan Miocene loess-soil se-quence is presented. Results show that mollusk species are abundant in the QA-I section between 22 and 6.2 Ma, and both loess layers...The first near continuous mollusk fossil record from the Qinan Miocene loess-soil se-quence is presented. Results show that mollusk species are abundant in the QA-I section between 22 and 6.2 Ma, and both loess layers and soil layers yield mollusk fossil individuals. All mollusk species are terrestrial and well preserved in the section. Most species are identical to those identified in the Quaternary loess-soil sequence of the Loess Plateau. The thermo-humidiphilous group generally is distributed in soil layers, whereas cold-aridiphilous group can be observed in loess layers. From the Miocene to Quaternary, the occurrence and divergence of new species of Metodontia and Cathaica correspond to the crucial periods of regional and global environmental changes, indicating that mol-lusk species are sensitive to environmental variations. Preliminary study on the QA-I mollusk record indicates that the Qinan Miocene loess-soil sequence may have a similar sedimentary environment to the Quaternary loess-soil sequence of the Loess Plateau.展开更多
The North China Craton(NCC)is a classic case of the destruction of an ancient craton,in that it records the loss of more than 100 km of ancient refractory lithospheric mantle during the Mesozoic(e.g.,Menzies et al.,19...The North China Craton(NCC)is a classic case of the destruction of an ancient craton,in that it records the loss of more than 100 km of ancient refractory lithospheric mantle during the Mesozoic(e.g.,Menzies et al.,1993).This展开更多
Hydrographic data, ADCP velocity and sea level anomaly derived from the satellite altimeter have been jointly analyzed in the southeast lndian Ocean. Results show the locations and orientations of the major oceanic fr...Hydrographic data, ADCP velocity and sea level anomaly derived from the satellite altimeter have been jointly analyzed in the southeast lndian Ocean. Results show the locations and orientations of the major oceanic fronts as well as the characteristics of the currents within these fronts in the area. Double subtropical fronts are observed in the section along 120°E, which conflicts with the frontal structure frequently observed before the North Subtropical Front （NSTF） and South Subtropical Front （SSTF） merge into a single STF between 110°-115°E. The Subantarctic Front （SAF）, influenced by the out-of-phase double eddies, runs across 48°S three times between 120° and 127°E. The surface current within the SAF is strengthened up to 105.4 cm/s by the geostrophic effect of these eddies. Furthermore eddies may cause the strong current to split up into two branches within the SAF. The SAF and the primary polar front （PFI） can be identified individually in the ADCP data with a separation distance of about 0.3° at latitude between 140° and 145°E, although they cannot be identified separately in the low-resolution hydrographic data. The different thcrmohaline characteristics of Circumpolar Deep Water （CDW） and Modified Circumpolar Deep Water （MCDW） result in the formation of Southern Antarctic Circumpolar Current Front （SACCF） in the southeast Indian Ocean. It consistently turns northward along the east flank of the Kerguclen Plateau after it runs through the Princess Elizabeth Trough and turns southward sharply north of 60°S with a little seasonal variations. It is shown that the locations and orientations of the SAK the primary PF and SACCF in the ACC of the southeast Indian Ocean can be identified more precisely by the current distribution derived from ADCP data than by hydrographic data, because these fronts are usually accompanied by strong currents. However, the locations and orientations of the STF and the secondary PF are more difficult to be identified through current data,展开更多
The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise loc...The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise locations of earthquakes since 1968, geodetic data and fault offsets for the 1906 great shock are used to re-examine the timing and locations of possible future large earthquakes. The physical mechanisms of regional faults like the Calaveras, Hayward and Sargent, which exhibit creep, differ from those of the northern San Andreas, which is currently locked and is not creeping. Much decadal forerunning activity occurred on creeping faults. Moderate-size earthquakes along those faults became more frequent as stresses in the region increased in the latter part of the cycle of stress restoration for major and great earthquakes along the San Andreas. They may be useful for decadal forecasts. Yearly to decadal forecasts, however, are based on only a few major to great events. Activity along closer faults like that in the two years prior to the 1989 Loma Prieta shock needs to be examined for possible yearly forerunning changes to large plate boundary earthquakes. Geodetic observations are needed to focus on identifying creeping faults close to the San Andreas. The distribution of moderate-size earthquakes increased significantly since 1990 along the Hayward fault but not adjacent to the San Andreas fault to the south of San Francisco compared to what took place in the decades prior to the three major historic earthquakes in the region. It is now clear from a re-examination of the 1989 mainshock that the increased level of moderate-size shocks in the one to two preceding decades occurred on nearby East Bay faults. Double-difference locations of small earthquakes provide structural information about faults in the region, especially their depths. The northern San Andreas fault is divided into several strongly coupled segments based on differences in seismicity.展开更多
This review describes advances in understanding and forecasting tropical cyclone(TC)subseasonal variability during the past four years.A large effort by the scientific community has been in understanding the sources of...This review describes advances in understanding and forecasting tropical cyclone(TC)subseasonal variability during the past four years.A large effort by the scientific community has been in understanding the sources of predictability at subseasonal timescales beyond the well-known modulation of TC activity by the Madden-Julian Oscillation(MJO).In particular,the strong modulation of TC activity over the western North Pacific by the Boreal Summer Intra-Seasonal Oscillation(BSISO)has been documented.Progress has also been realized in understanding the role of tropical-extratropical interactions in improving subseasonal forecasts.In addition,several recent publications have shown that extratropical wave breaking may have a role in the genesis and development of TCs.Analyses of multi-model ensemble data sets such as the Subseasonal to Seasonal(S2S)and Subseasonal Experiment(SubX)have shown that the skill of S2S models in predicting the genesis of TCs varies strongly among models and regions but is often tied to their ability to simulate the MJO and its impacts.The skill in select models has led to an increase over the past four years in the number of forecasting centers issuing subseasonal TC forecasts using various techniques(statistical,statistical-dynamical and dynamical).More extensive verification studies have been published over the last four years,but often only for the North Atlantic and eastern North Pacific.展开更多
The Ujaragssuit Nunat layered(UNL)unit in the Itsaq Gneiss Complex,west Greenland,has been consid-ered to contain one of the oldest chromitites on Earth based on~ca.4.1 Ga Hadean whole rock Pt-Os model ages and ca.3.8...The Ujaragssuit Nunat layered(UNL)unit in the Itsaq Gneiss Complex,west Greenland,has been consid-ered to contain one of the oldest chromitites on Earth based on~ca.4.1 Ga Hadean whole rock Pt-Os model ages and ca.3.81 Ga zircon U-Pb age of the surrounding orthogneiss.This study obtained zircon from the chromitite within this unit as well as granitoid sheets that intruded into the UNL unit.In-situ U-Pb-Hf-O isotope measurements were made on the zircons.Zircons from both the chromitite and the intrusive granitoids show concordant U-Pb ages of ca.2.97-2.95 Ga.In contrast,Hf and 0 isotopic anal-yses indicate that zircons in the chromitites have a different origin from those in the intrusive granitoids.Zircons from granitoids yielded Th/U ratios higher than 0.2,initial Hf isotope ratios of 0.2805-0.2807(i.e,initial:Hf value of-11 to-5),andδ^(18)O values of mostly 6.0‰-7.0‰,which are typical for felsic igneous rocks in Archean continental crust.The least altered zircons from a chromitite exhibited initial Hf isotope ratios of 0.28078-0.28084(i.e.,initial:Hf value of-1.1 to-0.4),close the chondritic value at ca.3.0 Ga and the depleted mantle at ca.3.2 Ga.These zircons also haveδ^(18)O values of 4.2‰6.1‰which correspond to typical mantle values.The other chromitite zircons yielded Th/U ratios lower than 0.1,and Hf and 0 isotopic compositions ranging between the least altered zircons and the intrusive granitoid zir-cons.These results indicate that the zircons in the chromitites crystallized before or during the 2.97-2.95 Ga granitoid intrusion and most of the zircons were altered by subsequent metasomatism.Furthermore,the present results suggest that zircons in the chromitites originally had depleted Hf iso-topic compositions at ca.3.2-3.0 Ga.This can be explained by two different models of the evolution of the UNL unit.One is that if the UNL unit was formed at>3.81 Ga as previously thought,with the zircons in the chromitites subsequently being precipitated by ca.3.2-2.95 Ga during metamorphism or metaso-matism展开更多
基金the National Science Foundation of China through Grants Nos.40520140074,40136010(for G.Fang),40476016(for Z.Wei)partly supported by The National Science Foundation(U.S.A)through Grant OCE-02-19782 and ONR Grants Nos.014041.0698,014051—0272(for R.D.Susanto)partly supported b oNR through Grants 040611-8331,050303-7499(for Q.Zheng).
文摘The existing estimates of the volume transport from the Pacific Ocean to the South China Sea are summarized, showing an annual mean westward transport, with the Taiwan Strait outflow subtracted, of 3.5±2.0 Sv （1 Sv=-0^6 ma s^-1）. Results of a global ocean circulation model show an annual mean transport of 3.9 Sv from the Pacific to the Indian Ocean through the South China Sea. The boreal winter transport is larger and exhibits a South China Sea branch of the Pacific-to-Indian Ocean throughflow, which originates from the western Philippine Sea toward the Indonesian Seas through the South China Sea, as well as through the Karimata and Mindoro Straits. The southwestward current near the continental slope of the northern South China Sea is shown to be a combination of this branch and the interior circulation gyre. This winter branch can be confirmed by trajectories of satellite-tracked drifters, which clearly show a flow from the Luzon Strait to the Karimata Strait in winter. In summer, the flow in the Karimata Strait is reversed. Numerical model results indicate that the Pacific water can enter the South China Sea and exit toward the Sulu Sea, but no observational evidence is available. The roles of the throughiiow branch in the circulation, water properties and air-sea exchange of the South China Sea, and in enhancing and regulating the volume transport and reducing the heat transport of the Indonesian Throughflow, are discussed.
基金the National Science Foundation of China (Grant Nos. 40671191 and 90502008)the Innovation Team Project (Grant No. 40421101)+2 种基金the Program for New Century Excellent Talents in University (Grant No. NCET-05-0888)the Chinese 111 Project (Grant No. B06026)J. Gordon was supported by US National Science Foundation (Grant No. ATM-0402474)
文摘Ecological systems in the headwaters of the Yellow River, characterized by hash natural environmental conditions, are very vulnerable to climatic change. In the most recent decades, this area greatly attracted the public's attention for its more and more deteriorating environmental conditions. Based on tree-ring samples from the Xiqing Mountain and A'nyêmagên Mountains at the headwaters of the Yellow River in the Northeastern Tibetan Plateau, we reconstructed the minimum temperatures in the winter half year over the last 425 years and the maximum temperatures in the summer half year over the past 700 years in this region. The variation of minimum temperature in the winter half year during the time span of 1578―1940 was a relatively stable trend, which was followed by an abrupt warming trend since 1941. However, there is no significant warming trend for the maximum temperature in the summer half year over the 20th century. The asymmetric variation patterns between the minimum and maximum temperatures were observed in this study over the past 425 years. During the past 425 years, there are similar variation patterns between the minimum and maximum temperatures; however, the minimum temperatures vary about 25 years earlier compared to the maximum temperatures. If such a trend of variation patterns between the minimum and maximum temperatures over the past 425 years continues in the future 30 years, the maximum temperature in this region will increase significantly.
基金Supported by the National Key Basic Research and Development Project of China (Grant No. 2004CB418300)the National Basic Research Program of China (973 Program) (Grant No. 2007CB411505)+3 种基金Chinese COPES project (GYHY200706005)the National Natural Science Foundation of China (Grant No. 40475030)R. D’Arrigo acknowledges support from the National Science Foundation (Grant No. OCE 04-02474)Lamont-Doherty Earth Observatory Contrib. No. 7126
文摘A dipole structure anomaly in summer Arctic atmospheric variability is identified in this study, which is characterized by the second mode of empirical orthogonal function (EOF) analysis of summer monthly mean sea level pressure (SLP) north of 70°N, accounting for 12.94% of the variance. The dipole anom- aly shows a quasi-barotropic structure with opposite anomalous centers over the Canadian Arctic and the Beaufort Sea and between the Kara Sea and the Laptev Sea. The dipole anomaly reflects alternating variations in location of the polar vortex between the western and eastern Arctic regions. The positive phase of the dipole anomaly corresponds to the center of the polar vortex over the western Arctic, leading to an increase in summer mean rainfall in Northeast China. The dipole anomaly has a pre- dominant 6-year periodicity, and shows interdecadal variations in recent decades.
基金supported by the National Key R&D Program of China (2018YFA0605901)the NOAA Climate Program Office (NA15OAR4310163)+1 种基金the National Natural Science Foundation of China (41676185)and the Key Research Program of Frontier Sciences of Chinese Academy of Sciences (QYZDY-SSW-DQC021)
文摘Rapid declines in Arctic sea ice have captured attention and pose significant challenges to a variety of stakeholders. There is a rising demand for Arctic sea ice prediction at daily to seasonal time scales, which is partly a sea ice initial condition problem. Thus, a multivariate data assimilation that integrates sea ice observations to generate realistic and skillful model initialization is needed to improve predictive skill of Arctic sea ice. Sea ice data assimilation is a relatively new research area. In this review paper, we focus on two challenges for implementing multivariate data assimilation systems for sea ice forecast. First, to address the challenge of limited spatiotemporal coverage and large uncertainties of observations, we discuss sea ice parameters derived from satellite remote sensing that(1) have been utilized for improved model initialization, including concentration, thickness and drift, and(2) are currently under development with the potential for enhancing the predictability of Arctic sea ice, including melt ponds and sea ice leads. Second, to strive to generate the ‘‘best" estimate of sea ice initial conditions by combining model simulations/forecasts and observations, we review capabilities and limitations of different data assimilation techniques that have been developed and used to assimilate observed sea ice parameters in dynamical models.
文摘Recent tree-ring studies in Mongolia provide evidence of unusual warming that is in agreement with large-scale reconstructed and recorded temperatures for the Northern Hemisphere and the Arctic. One Mongolian proxy record for temperature extends back over 1000 years and several others are over 350 years in length. Precipitation reconstructions based on tree rings reflect recent increases but also indicate that the increases are within the long-term range of variations. Spectral analyses of recorded precipitation data and the reconstructions support the hypotheses of quasi-solar periodicity in precipitation variation, previously suggested by others.
基金The National Science Foundation of the United States under contract No.OCE-07-25935the Office of Naval Research of the United States under contract No.N00014-08-1-0618 (for US LDEO)+4 种基金the National Basic Research Program under contract No.2011CB403502the International Cooperation Program of China under contract No.2010DFB23580the International Cooperation Program of State Oceanic Administration of China under contract No.QY0213022the First Institute of Oceanography,the State Oceanic Administration of China under contract No.2010G06 (for Chinese researchers)the Lamont-Doherty Earth Obseruatory contribution No.7626
文摘In order to quantitatively estimate the volume and property transports between the South China Sea and Indonesian Seas via the Karimata Strait, two trawi-resistant bottom mounts, with ADCPs embedded, were deployed in the strait to measure the velocity profile as part of the South China Sea-Indonesian Seas trans- port/exchange （SITE） program. A pair of surface and bottom acoustic modems was employed to transfer the measured velocity without recovering the mooring. The advantage and problems of the instruments in this field work are reported and discussed. The field observations confirm the existence of the South Chi- na Sea branch of Indonesian throughflow via the Karimata Strait with a stronger southward flow in boreal winter and weaker southward bottom flow in boreal summer, beneath the upper layer northward （reversal） flow. The estimate of the averaged volume, heat and freshwater transports from December 2007 to March 2008 （winter） is （-2.7±1.1）×10^6 m^3/s, （-0.30±0.11） PW, 2008 （summer） is （1.2±0.6）×10^6 m^3/s, （0.14±0.03） PW, （-0.18±0.07） × 106 m3/s and from May to September （0.12±0.04）×10^6 m^3/s and for the entire record from December 2007 to October 2008 is （-0.5±1.9）×10^6 m^3/s, （-0.05±0.22） PW, （-0.01±0.15）×10^6 m^3/s （nega- tive/positive represents southward/northward transport）, respectively. The existence of southward bottom flow in boreal summer implies that the downward sea surface slope from north to south as found by Fang et al. （2010） for winter is a year-round phenomenon.
基金This work was supported by the National Basic Research Program of China(Grant No.2004CB720203)the National Natural Science Foundation of China(Grant Nos.40231001 and 40372083)the Chinese Academy of Sciences(Grant No.KZCX3-SW-139).
文摘The first near continuous mollusk fossil record from the Qinan Miocene loess-soil se-quence is presented. Results show that mollusk species are abundant in the QA-I section between 22 and 6.2 Ma, and both loess layers and soil layers yield mollusk fossil individuals. All mollusk species are terrestrial and well preserved in the section. Most species are identical to those identified in the Quaternary loess-soil sequence of the Loess Plateau. The thermo-humidiphilous group generally is distributed in soil layers, whereas cold-aridiphilous group can be observed in loess layers. From the Miocene to Quaternary, the occurrence and divergence of new species of Metodontia and Cathaica correspond to the crucial periods of regional and global environmental changes, indicating that mol-lusk species are sensitive to environmental variations. Preliminary study on the QA-I mollusk record indicates that the Qinan Miocene loess-soil sequence may have a similar sedimentary environment to the Quaternary loess-soil sequence of the Loess Plateau.
文摘The North China Craton(NCC)is a classic case of the destruction of an ancient craton,in that it records the loss of more than 100 km of ancient refractory lithospheric mantle during the Mesozoic(e.g.,Menzies et al.,1993).This
基金the National Natural Science Foundation of China undrer contract Nos 40376009, 40231013 ,49836010 the Ministry of Science and Technology of China under contract Nos 2003DIB4J135 , 2005DIB3J114the National Science Foundation of USA under contract No. 0PP0230284.
文摘Hydrographic data, ADCP velocity and sea level anomaly derived from the satellite altimeter have been jointly analyzed in the southeast lndian Ocean. Results show the locations and orientations of the major oceanic fronts as well as the characteristics of the currents within these fronts in the area. Double subtropical fronts are observed in the section along 120°E, which conflicts with the frontal structure frequently observed before the North Subtropical Front （NSTF） and South Subtropical Front （SSTF） merge into a single STF between 110°-115°E. The Subantarctic Front （SAF）, influenced by the out-of-phase double eddies, runs across 48°S three times between 120° and 127°E. The surface current within the SAF is strengthened up to 105.4 cm/s by the geostrophic effect of these eddies. Furthermore eddies may cause the strong current to split up into two branches within the SAF. The SAF and the primary polar front （PFI） can be identified individually in the ADCP data with a separation distance of about 0.3° at latitude between 140° and 145°E, although they cannot be identified separately in the low-resolution hydrographic data. The different thcrmohaline characteristics of Circumpolar Deep Water （CDW） and Modified Circumpolar Deep Water （MCDW） result in the formation of Southern Antarctic Circumpolar Current Front （SACCF） in the southeast Indian Ocean. It consistently turns northward along the east flank of the Kerguclen Plateau after it runs through the Princess Elizabeth Trough and turns southward sharply north of 60°S with a little seasonal variations. It is shown that the locations and orientations of the SAK the primary PF and SACCF in the ACC of the southeast Indian Ocean can be identified more precisely by the current distribution derived from ADCP data than by hydrographic data, because these fronts are usually accompanied by strong currents. However, the locations and orientations of the STF and the secondary PF are more difficult to be identified through current data,
文摘The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise locations of earthquakes since 1968, geodetic data and fault offsets for the 1906 great shock are used to re-examine the timing and locations of possible future large earthquakes. The physical mechanisms of regional faults like the Calaveras, Hayward and Sargent, which exhibit creep, differ from those of the northern San Andreas, which is currently locked and is not creeping. Much decadal forerunning activity occurred on creeping faults. Moderate-size earthquakes along those faults became more frequent as stresses in the region increased in the latter part of the cycle of stress restoration for major and great earthquakes along the San Andreas. They may be useful for decadal forecasts. Yearly to decadal forecasts, however, are based on only a few major to great events. Activity along closer faults like that in the two years prior to the 1989 Loma Prieta shock needs to be examined for possible yearly forerunning changes to large plate boundary earthquakes. Geodetic observations are needed to focus on identifying creeping faults close to the San Andreas. The distribution of moderate-size earthquakes increased significantly since 1990 along the Hayward fault but not adjacent to the San Andreas fault to the south of San Francisco compared to what took place in the decades prior to the three major historic earthquakes in the region. It is now clear from a re-examination of the 1989 mainshock that the increased level of moderate-size shocks in the one to two preceding decades occurred on nearby East Bay faults. Double-difference locations of small earthquakes provide structural information about faults in the region, especially their depths. The northern San Andreas fault is divided into several strongly coupled segments based on differences in seismicity.
基金NOAA through the Cooperative Institute for Satellite Earth System Studies under Cooperative Agreement NA19NES4320002.Janiga acknowledges the support of the Chief of Naval Research through the NRL Base Program PE 62435N.Camargo and Lee acknowledge support from the NASA MAP program(80NSSC21K1495)Camargo also acknowledges support from NOAA(NA22OAR4310610)the Vetlesen Foundation.Wang was supported by the National Science Foundation under Grant No.2116804。
文摘This review describes advances in understanding and forecasting tropical cyclone(TC)subseasonal variability during the past four years.A large effort by the scientific community has been in understanding the sources of predictability at subseasonal timescales beyond the well-known modulation of TC activity by the Madden-Julian Oscillation(MJO).In particular,the strong modulation of TC activity over the western North Pacific by the Boreal Summer Intra-Seasonal Oscillation(BSISO)has been documented.Progress has also been realized in understanding the role of tropical-extratropical interactions in improving subseasonal forecasts.In addition,several recent publications have shown that extratropical wave breaking may have a role in the genesis and development of TCs.Analyses of multi-model ensemble data sets such as the Subseasonal to Seasonal(S2S)and Subseasonal Experiment(SubX)have shown that the skill of S2S models in predicting the genesis of TCs varies strongly among models and regions but is often tied to their ability to simulate the MJO and its impacts.The skill in select models has led to an increase over the past four years in the number of forecasting centers issuing subseasonal TC forecasts using various techniques(statistical,statistical-dynamical and dynamical).More extensive verification studies have been published over the last four years,but often only for the North Atlantic and eastern North Pacific.
基金supported by JSPS KAKENHI Grant Numbers 16H05741,19KK0092Kana-zawa SAKIGAKE 2018 to T.M.,and 20 K14571 to H.S..K.S.thanks the Carlsberg Foundation for support via grant CF18-0090.
文摘The Ujaragssuit Nunat layered(UNL)unit in the Itsaq Gneiss Complex,west Greenland,has been consid-ered to contain one of the oldest chromitites on Earth based on~ca.4.1 Ga Hadean whole rock Pt-Os model ages and ca.3.81 Ga zircon U-Pb age of the surrounding orthogneiss.This study obtained zircon from the chromitite within this unit as well as granitoid sheets that intruded into the UNL unit.In-situ U-Pb-Hf-O isotope measurements were made on the zircons.Zircons from both the chromitite and the intrusive granitoids show concordant U-Pb ages of ca.2.97-2.95 Ga.In contrast,Hf and 0 isotopic anal-yses indicate that zircons in the chromitites have a different origin from those in the intrusive granitoids.Zircons from granitoids yielded Th/U ratios higher than 0.2,initial Hf isotope ratios of 0.2805-0.2807(i.e,initial:Hf value of-11 to-5),andδ^(18)O values of mostly 6.0‰-7.0‰,which are typical for felsic igneous rocks in Archean continental crust.The least altered zircons from a chromitite exhibited initial Hf isotope ratios of 0.28078-0.28084(i.e.,initial:Hf value of-1.1 to-0.4),close the chondritic value at ca.3.0 Ga and the depleted mantle at ca.3.2 Ga.These zircons also haveδ^(18)O values of 4.2‰6.1‰which correspond to typical mantle values.The other chromitite zircons yielded Th/U ratios lower than 0.1,and Hf and 0 isotopic compositions ranging between the least altered zircons and the intrusive granitoid zir-cons.These results indicate that the zircons in the chromitites crystallized before or during the 2.97-2.95 Ga granitoid intrusion and most of the zircons were altered by subsequent metasomatism.Furthermore,the present results suggest that zircons in the chromitites originally had depleted Hf iso-topic compositions at ca.3.2-3.0 Ga.This can be explained by two different models of the evolution of the UNL unit.One is that if the UNL unit was formed at>3.81 Ga as previously thought,with the zircons in the chromitites subsequently being precipitated by ca.3.2-2.95 Ga during metamorphism or metaso-matism
