2012 Vol. 31, No. 5
Display Method:
2012, (5): 1-10.
doi: 10.1007/s13131-012-0231-y
Abstract:
The advances in understanding the South China Sea (SCS) western boundary current (SCSwbc) have been reviewed since the works of Dale (1956) and Wyrtki (1961) in the middle of the 20th century. The features of the pattern of SCSwbc and the oceanic phenomena associated with it are focused on. The current is driven mainly by monsoon over the SCS and partially by winds over the tropical Pacific governed by the island rule. The SCSwbc exhibits strong seasonal variation in its direction and patterns. In winter, the current is strong and flows southwestward along the South China shelf and slope from the east of Dongsha Islands to the northern central Vietnamese coast, then turns to the south along the central and southern Vietnamese coast, and finally partially exits the SCS through the Karimata Strait. In summer and early fall, the SCSwbc can be divided into three segments based on their characteristics. The southern segment is stable, flowing northward from the Karimata Strait up to about 11°N, where it separates from the coast forming an eastward offshore current. The separation of the current from Vietnamese coast induces some striking features, such as upwelling and cold sea-surface temperature. The middle segment off the central Vietnamese coast may have a bimodal behavior:northward coastal current and meandering current in early summer (June-July), and cyclonic gyre in later summer and early fall (August-September). The northern segment is featured by the summer SCS Warm Current on the South China shelf and a southwestward subsurface current along the continental slope.
The advances in understanding the South China Sea (SCS) western boundary current (SCSwbc) have been reviewed since the works of Dale (1956) and Wyrtki (1961) in the middle of the 20th century. The features of the pattern of SCSwbc and the oceanic phenomena associated with it are focused on. The current is driven mainly by monsoon over the SCS and partially by winds over the tropical Pacific governed by the island rule. The SCSwbc exhibits strong seasonal variation in its direction and patterns. In winter, the current is strong and flows southwestward along the South China shelf and slope from the east of Dongsha Islands to the northern central Vietnamese coast, then turns to the south along the central and southern Vietnamese coast, and finally partially exits the SCS through the Karimata Strait. In summer and early fall, the SCSwbc can be divided into three segments based on their characteristics. The southern segment is stable, flowing northward from the Karimata Strait up to about 11°N, where it separates from the coast forming an eastward offshore current. The separation of the current from Vietnamese coast induces some striking features, such as upwelling and cold sea-surface temperature. The middle segment off the central Vietnamese coast may have a bimodal behavior:northward coastal current and meandering current in early summer (June-July), and cyclonic gyre in later summer and early fall (August-September). The northern segment is featured by the summer SCS Warm Current on the South China shelf and a southwestward subsurface current along the continental slope.
2012, (5): 11-25.
doi: 10.1007/s13131-012-0232-x
Abstract:
The sea-level anomaly (SLA) from a satellite altimeter has a high accuracy and can be used to improve ocean state estimation by assimilation techniques. However, the lack of an accurate mean dynamic topography (MDT) is still a bothersome issue in an ocean data assimilation. The previous studies showed that the errors in MDT have significant impacts on assimilation results, especially on the time-mean components of ocean states and on the time variant parts of states via nonlinear ocean dynamics. The temporal-spatial differences of three MDTs and their impacts on the SLA analysis are focused on in the South China Sea (SCS). The theoretical analysis shows that even for linear models, the errors in MDT have impacts on the SLA analysis using a sequential data assimilation scheme. Assimilation experiments, based on EnOI scheme and HYCOM, with three MDTs from July 2003 to June 2004 also show that the SLA assimilation is very sensitive to the choice of different MDTs in the SCS with obvious differences between the experimental results and observations in the centre of the SCS and in the vicinity of the Philippine Islands. A new MDT for assimilation of SLA data in the SCS was proposed. The results from the assimilation experiment with this new MDT show a marked reduction (increase) in the RMSEs (correlation coefficient) between the experimental and observed SLA. Furthermore, the subsurface temperature field is also improved with this new MDT in the SCS.
The sea-level anomaly (SLA) from a satellite altimeter has a high accuracy and can be used to improve ocean state estimation by assimilation techniques. However, the lack of an accurate mean dynamic topography (MDT) is still a bothersome issue in an ocean data assimilation. The previous studies showed that the errors in MDT have significant impacts on assimilation results, especially on the time-mean components of ocean states and on the time variant parts of states via nonlinear ocean dynamics. The temporal-spatial differences of three MDTs and their impacts on the SLA analysis are focused on in the South China Sea (SCS). The theoretical analysis shows that even for linear models, the errors in MDT have impacts on the SLA analysis using a sequential data assimilation scheme. Assimilation experiments, based on EnOI scheme and HYCOM, with three MDTs from July 2003 to June 2004 also show that the SLA assimilation is very sensitive to the choice of different MDTs in the SCS with obvious differences between the experimental results and observations in the centre of the SCS and in the vicinity of the Philippine Islands. A new MDT for assimilation of SLA data in the SCS was proposed. The results from the assimilation experiment with this new MDT show a marked reduction (increase) in the RMSEs (correlation coefficient) between the experimental and observed SLA. Furthermore, the subsurface temperature field is also improved with this new MDT in the SCS.
2012, (5): 26-40.
doi: 10.1007/s13131-012-0233-9
Abstract:
The mesoscale eddy and internal wave both are phenomena commonly observed in oceans. It is aimed to investigate how the presence of a mesoscale eddy in the ocean affects wave form deformation of the internal solitary wave propagation. An ocean eddy is produced by a quasi-geostrophic model in f-plane, and the one-dimensional nonlinear variable-coefficient extended Korteweg-de Vries (eKdV) equation is used to simulate an internal solitary wave passing through the mesoscale eddy field. The results suggest that the mode structures of the linear internal wave are modified due to the presence of the mesoscale eddy field. A cyclonic eddy and an anticyclonic eddy have different influences on the background environment of the internal solitary wave propagation. The existence of a mesoscale eddy field has almost no prominent impact on the propagation of a smallamplitude internal solitary wave only based on the first mode vertical structure, but the mesoscale eddy background field exerts a considerable influence on the solitary wave propagation if considering high-mode vertical structures. Furthermore, whether an internal solitary wave first passes through anticyclonic eddy or cyclonic eddy, the deformation of wave profiles is different. Many observations of solitary internal waves in the real oceans suggest the formation of the waves. Apart from topography effect, it is shown that the mesoscale eddy background field is also a considerable factor which influences the internal solitary wave propagation and deformation.
The mesoscale eddy and internal wave both are phenomena commonly observed in oceans. It is aimed to investigate how the presence of a mesoscale eddy in the ocean affects wave form deformation of the internal solitary wave propagation. An ocean eddy is produced by a quasi-geostrophic model in f-plane, and the one-dimensional nonlinear variable-coefficient extended Korteweg-de Vries (eKdV) equation is used to simulate an internal solitary wave passing through the mesoscale eddy field. The results suggest that the mode structures of the linear internal wave are modified due to the presence of the mesoscale eddy field. A cyclonic eddy and an anticyclonic eddy have different influences on the background environment of the internal solitary wave propagation. The existence of a mesoscale eddy field has almost no prominent impact on the propagation of a smallamplitude internal solitary wave only based on the first mode vertical structure, but the mesoscale eddy background field exerts a considerable influence on the solitary wave propagation if considering high-mode vertical structures. Furthermore, whether an internal solitary wave first passes through anticyclonic eddy or cyclonic eddy, the deformation of wave profiles is different. Many observations of solitary internal waves in the real oceans suggest the formation of the waves. Apart from topography effect, it is shown that the mesoscale eddy background field is also a considerable factor which influences the internal solitary wave propagation and deformation.
2012, (5): 41-45.
doi: 10.1007/s13131-012-0234-8
Abstract:
The previous studies show that the spreading path of the subtropical salinity minimum of the North Pacific Intermediate Water (NPIW) is southwestward pointing to the Luzon Strait. Based on the P-vector method and generalized digital environmental model (GDEM) data, the volume transport of NPIW through Luzon Strait and the upward transport on the NPIW lower and upper boundaries are calculated to examine the destiny of NPIW in the South China Sea (SCS). On the annual mean, the estimation of NPIW transport into the SCS through the Luzon Strait is 1.72 Sv (1Sv=106 m3/s). The upward transport over the SCS is 0.31 Sv on the NPIW upper boundary and 1.31 Sv on the NPIW lower boundary. There is no strait or passage deeper than the surface for the NPIW to extend, except for the Luzon Strait. For the volume balance in the SCS NPIW, the volume transport of 2.72 Sv has to flow out of the SCS NPIW layer through the Luzon Strait.
The previous studies show that the spreading path of the subtropical salinity minimum of the North Pacific Intermediate Water (NPIW) is southwestward pointing to the Luzon Strait. Based on the P-vector method and generalized digital environmental model (GDEM) data, the volume transport of NPIW through Luzon Strait and the upward transport on the NPIW lower and upper boundaries are calculated to examine the destiny of NPIW in the South China Sea (SCS). On the annual mean, the estimation of NPIW transport into the SCS through the Luzon Strait is 1.72 Sv (1Sv=106 m3/s). The upward transport over the SCS is 0.31 Sv on the NPIW upper boundary and 1.31 Sv on the NPIW lower boundary. There is no strait or passage deeper than the surface for the NPIW to extend, except for the Luzon Strait. For the volume balance in the SCS NPIW, the volume transport of 2.72 Sv has to flow out of the SCS NPIW layer through the Luzon Strait.
2012, (5): 46-53.
doi: 10.1007/s13131-012-0235-7
Abstract:
Seismic oceanography is a new cross-discipline of reflection seismology and physical oceanography. The biggest difference between seismic oceanography and traditional reflection seismology is its research object of time-varied seawater. How to estimate the temporal variations of reflectors in water structure and make some corrections in seismic data are basic problems in seismic oceanography research. Here a method of estimation for seawater movement is provided based on the reflectors. The application results of this method to the simulated and field seismic data turn out to be acceptable. As compared with the previous research, this method has the advantages of low-dependence on migration velocity and dip of reflectors, and it is very suitable for correction in a spectral analysis using seismic data, which is very useful in the research of ocean energy budget.
Seismic oceanography is a new cross-discipline of reflection seismology and physical oceanography. The biggest difference between seismic oceanography and traditional reflection seismology is its research object of time-varied seawater. How to estimate the temporal variations of reflectors in water structure and make some corrections in seismic data are basic problems in seismic oceanography research. Here a method of estimation for seawater movement is provided based on the reflectors. The application results of this method to the simulated and field seismic data turn out to be acceptable. As compared with the previous research, this method has the advantages of low-dependence on migration velocity and dip of reflectors, and it is very suitable for correction in a spectral analysis using seismic data, which is very useful in the research of ocean energy budget.
2012, (5): 54-68.
doi: 10.1007/s13131-012-0236-6
Abstract:
The modulation of tropical cyclogenesis over the southern South China Sea (SSCS) by the El Niño-Southern Oscillation (ENSO) is examined in October-December (OND), when tropical cyclone (TC) activities are most active in this region. The results reveal that there were more TCs formed over the SSCS during La Niña years and less TCs during El Niño years. How different environmental factors (including low-level vorticity, mid-level relative humidity, vertical wind shear, and potential intensity) contribute to this influence is investigated, using a genesis potential (GP) index developed by Emanuel and Nolan. Composite anomalies of the GP index are produced for El Niño and La Niña years separately, which could account for the changes of TC frequency over the SSCS in different ENSO phases. The degree of contribution by each factor is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. The results show that the mid-level relative humidity makes the largest contribution to the ENSO modulation of tropical cyclogenesis over the SSCS. Although warmer sea surface temperatures (SSTs) and larger amount of evaporation from the ocean surface were observed over the SSCS during El Niño years, anomalous descending motions due to the anomalous Walker circulations inhibited the upward transports of water vapor and led to less moisture contents in the middle troposphere, which suppressed TC formations.
The modulation of tropical cyclogenesis over the southern South China Sea (SSCS) by the El Niño-Southern Oscillation (ENSO) is examined in October-December (OND), when tropical cyclone (TC) activities are most active in this region. The results reveal that there were more TCs formed over the SSCS during La Niña years and less TCs during El Niño years. How different environmental factors (including low-level vorticity, mid-level relative humidity, vertical wind shear, and potential intensity) contribute to this influence is investigated, using a genesis potential (GP) index developed by Emanuel and Nolan. Composite anomalies of the GP index are produced for El Niño and La Niña years separately, which could account for the changes of TC frequency over the SSCS in different ENSO phases. The degree of contribution by each factor is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. The results show that the mid-level relative humidity makes the largest contribution to the ENSO modulation of tropical cyclogenesis over the SSCS. Although warmer sea surface temperatures (SSTs) and larger amount of evaporation from the ocean surface were observed over the SSCS during El Niño years, anomalous descending motions due to the anomalous Walker circulations inhibited the upward transports of water vapor and led to less moisture contents in the middle troposphere, which suppressed TC formations.
2012, (5): 69-78.
doi: 10.1007/s13131-012-0237-5
Abstract:
Using surface and aerological meteorological observations obtained at the Xisha Automatic Weather Station and three moored buoys along the continental slope, characteristics of the synoptic-scale disturbances over the northern South China Sea (NSCS) are extensively studied. The power spectra of surface and aerological observations suggest a synoptic feature with a pronounced energy peak at a period of 5-8 d and a weak peak at 3-4 d. The standard deviation of the synoptic temperature component derived at Xisha Station from 1976 to 2011 indicates that the strongest variability normally exists in August all through the whole troposphere. At the interannual scale, it is found that El Niño plays an important role in regulating the synoptic disturbances of atmosphere. The vertical synoptic disturbances have a double active peak following El Niño condition. The first peak usually occurs during the mature phase of El Niño, and the second one occurs in the summer of decay year. Comparing with the summer of developing years, the summer of the decaying year of El Niño has more active and stronger synoptic disturbances, especially for the 5-8 d period variations.
Using surface and aerological meteorological observations obtained at the Xisha Automatic Weather Station and three moored buoys along the continental slope, characteristics of the synoptic-scale disturbances over the northern South China Sea (NSCS) are extensively studied. The power spectra of surface and aerological observations suggest a synoptic feature with a pronounced energy peak at a period of 5-8 d and a weak peak at 3-4 d. The standard deviation of the synoptic temperature component derived at Xisha Station from 1976 to 2011 indicates that the strongest variability normally exists in August all through the whole troposphere. At the interannual scale, it is found that El Niño plays an important role in regulating the synoptic disturbances of atmosphere. The vertical synoptic disturbances have a double active peak following El Niño condition. The first peak usually occurs during the mature phase of El Niño, and the second one occurs in the summer of decay year. Comparing with the summer of developing years, the summer of the decaying year of El Niño has more active and stronger synoptic disturbances, especially for the 5-8 d period variations.
2012, (5): 79-86.
doi: 10.1007/s13131-012-0238-4
Abstract:
The seasonal variabilities of a latent-heat flux (LHF), a sensible-heat flux (SHF) and net surface heat flux are examined in the northern South China Sea (NSCS), including their spatial characteristics, using the in situ data collected by ship from 2006 to 2007. The spatial distribution of LHF in the NSCS is mostly controlled by wind in summer and autumn owing to the lower vertical gradient of air humidity, but is influenced by both wind and near-surface air humidity vertical gradient in spring and winter. The largest area-averaged LHF is in autumn, with the value of 197.25 W/m2, followed by that in winter; the third and the forth are in summer and spring, respectively. The net heat flux is positive in spring and summer, so the NSCS absorbs heat; and the solar shortwave radiation plays the most important role in the surface heat budget. In autumn and winter, the net heat flux is negative in most of the observation region, so the NSCS loses heat; and the LHF plays the most important role in the surface heat budget. The net heating is mainly a result of the offsetting between heating due to the shortwave radiation and cooling due to the LHF and the upward (outgoing) long wave radiation, since the role of SHF is negligible. The ratio of the magnitudes of the three terms (shortwave radiation to LHF to long-wave radiation) averaged over the entire year is roughly 3:2:1, and the role of SHF is the smallest.
The seasonal variabilities of a latent-heat flux (LHF), a sensible-heat flux (SHF) and net surface heat flux are examined in the northern South China Sea (NSCS), including their spatial characteristics, using the in situ data collected by ship from 2006 to 2007. The spatial distribution of LHF in the NSCS is mostly controlled by wind in summer and autumn owing to the lower vertical gradient of air humidity, but is influenced by both wind and near-surface air humidity vertical gradient in spring and winter. The largest area-averaged LHF is in autumn, with the value of 197.25 W/m2, followed by that in winter; the third and the forth are in summer and spring, respectively. The net heat flux is positive in spring and summer, so the NSCS absorbs heat; and the solar shortwave radiation plays the most important role in the surface heat budget. In autumn and winter, the net heat flux is negative in most of the observation region, so the NSCS loses heat; and the LHF plays the most important role in the surface heat budget. The net heating is mainly a result of the offsetting between heating due to the shortwave radiation and cooling due to the LHF and the upward (outgoing) long wave radiation, since the role of SHF is negligible. The ratio of the magnitudes of the three terms (shortwave radiation to LHF to long-wave radiation) averaged over the entire year is roughly 3:2:1, and the role of SHF is the smallest.
2012, (5): 87-97.
doi: 10.1007/s13131-012-0239-3
Abstract:
A global ocean carbon cycle model based on the ocean general circulation model POP and the improved biogeochemical model OCMIP-2 is employed to simulate carbon cycle processes under the historically observed atmospheric CO2 concentration and different future scenarios (called Representative Concentration Pathways, or RCPs). The RCPs in this paper follow the design of Intergovernmental Panel on Climate Change (IPCC) for the Fifth Assessment Report (AR5). The model results show that the ocean absorbs CO2 from atmosphere and the absorbability will continue in the 21st century under the four RCPs. The net air-sea CO2 flux increased during the historical time and reached 1.87 Pg/a (calculated by carbon) in 2005; however, it would reach peak and then decrease in the 21st century. The ocean absorbs CO2 mainly in the mid latitude, and releases CO2 in the equator area. However, in the Antarctic Circumpolar Current (ACC) area the ocean would change from source to sink under the rising CO2 concentration, including RCP4.5, RCP6.0, and RCP8.5. In 2100, the anthropogenic carbon would be transported to the 40°S in the Atlantic Ocean by the North Atlantic Deep Water (NADW), and also be transported to the north by the Antarctic Bottom Water (AABW) along the Antarctic continent in the Atlantic and Pacific oceans. The ocean pH value is also simulated by the model. The pH decreased by 0.1 after the industrial revolution, and would continue to decrease in the 21st century. For the highest concentration scenario of RCP8.5, the global averaged pH would decrease by 0.43 to reach 7.73 due to the absorption of CO2 from atmosphere.
A global ocean carbon cycle model based on the ocean general circulation model POP and the improved biogeochemical model OCMIP-2 is employed to simulate carbon cycle processes under the historically observed atmospheric CO2 concentration and different future scenarios (called Representative Concentration Pathways, or RCPs). The RCPs in this paper follow the design of Intergovernmental Panel on Climate Change (IPCC) for the Fifth Assessment Report (AR5). The model results show that the ocean absorbs CO2 from atmosphere and the absorbability will continue in the 21st century under the four RCPs. The net air-sea CO2 flux increased during the historical time and reached 1.87 Pg/a (calculated by carbon) in 2005; however, it would reach peak and then decrease in the 21st century. The ocean absorbs CO2 mainly in the mid latitude, and releases CO2 in the equator area. However, in the Antarctic Circumpolar Current (ACC) area the ocean would change from source to sink under the rising CO2 concentration, including RCP4.5, RCP6.0, and RCP8.5. In 2100, the anthropogenic carbon would be transported to the 40°S in the Atlantic Ocean by the North Atlantic Deep Water (NADW), and also be transported to the north by the Antarctic Bottom Water (AABW) along the Antarctic continent in the Atlantic and Pacific oceans. The ocean pH value is also simulated by the model. The pH decreased by 0.1 after the industrial revolution, and would continue to decrease in the 21st century. For the highest concentration scenario of RCP8.5, the global averaged pH would decrease by 0.43 to reach 7.73 due to the absorption of CO2 from atmosphere.
2012, (5): 98-106.
doi: 10.1007/s13131-012-0240-x
Abstract:
Spatial and temporal variability of the absorption properties of colored dissolved organic matter (CDOM) in the Taiwan Strait was investigated in summer (July to August of 2006) and winter (from December 2006 to January of 2007) seasons. The CDOM absorption coefficient at 280 nm (a280) showed a decreasing trend from nearshore to offshore areas while the spectral slope coefficient parameter calculated between wavelengths 275-295 nm (S275-295) showed an increase, indicative of decreasing aromaticity and molecular weight of the CDOM. The average a280 in winter (1.47±0.50 m-1) was significantly higher than in summer (1.10±0.41 m-1), while the average S275-295 in winter (26.7±5.2 μm-1) was significantly lower than in summer (30.6±5.5 μm-1), demonstrating clear seasonal variation in CDOM abundance and properties in the Taiwan Strait. A three-endmember conservative mixing model showed that local terrestrial CDOM inputs from several rivers along the western coast were small (<5%). However, the distribution of CDOM in the Taiwan Strait is mainly controlled by water mass movement[i.e., the Zhe-min Coastal Current (ZCC) and the Kuroshio Branch Current (KBC) in winter and the South China Sea Water (SCSW) in summer]. Biological activity was also an important factor affecting the distribution of CDOM in the offshore region in summer months.
Spatial and temporal variability of the absorption properties of colored dissolved organic matter (CDOM) in the Taiwan Strait was investigated in summer (July to August of 2006) and winter (from December 2006 to January of 2007) seasons. The CDOM absorption coefficient at 280 nm (a280) showed a decreasing trend from nearshore to offshore areas while the spectral slope coefficient parameter calculated between wavelengths 275-295 nm (S275-295) showed an increase, indicative of decreasing aromaticity and molecular weight of the CDOM. The average a280 in winter (1.47±0.50 m-1) was significantly higher than in summer (1.10±0.41 m-1), while the average S275-295 in winter (26.7±5.2 μm-1) was significantly lower than in summer (30.6±5.5 μm-1), demonstrating clear seasonal variation in CDOM abundance and properties in the Taiwan Strait. A three-endmember conservative mixing model showed that local terrestrial CDOM inputs from several rivers along the western coast were small (<5%). However, the distribution of CDOM in the Taiwan Strait is mainly controlled by water mass movement[i.e., the Zhe-min Coastal Current (ZCC) and the Kuroshio Branch Current (KBC) in winter and the South China Sea Water (SCSW) in summer]. Biological activity was also an important factor affecting the distribution of CDOM in the offshore region in summer months.
2012, (5): 107-114.
doi: 10.1007/s13131-012-0241-9
Abstract:
Drilling wells reveal that the organic matter abundance of Miocene marine source rocks in shallow water area of the Qiongdongnan Basin is relatively low with poor hydrocarbon generation potential. However, in some drilling wells of deep water area close to the central depression belt, Miocene marine source rocks with better organic matter abundance and hydrocarbon generation have been found, which have achieved better source rock standard based on the analysis of geochemical characteristics. Although there are no exploratory wells in deep water area of the research region, through the comparative analysis of geochemical data of several typical exploratory wells respectively from shallow water area in the basin, central depression belt margin in deep-water area of the basin and Site 1148 of deep sea drilling in the South China Sea Basin, it reveals that the tendency of the quality of source rocks becomes positive gradually from delta to bathyal environment, which then becomes negative as in deep oceanic environment. Owing to the lack of terrestrial organic matter input, the important controlling factors of Miocene marine source rocks in the Qiongdongnan Basin are ocean productivity and preservation conditions of organic matter. The element geochemistry data indicate that the tendency of the paleoproductivity and the preservation conditions of organic matter become positive as water depth increase from shallow area to bathyal area close to central depression belt. So it is speculated that there must exist high quality source rocks in the central depression area where the preservation conditions of organic matter are much better. Besides, in theory, in oxygen-poor zone of oceanic environment at the water depth 400-1 000 m, the preservation conditions of organic matter are well thus forming high-quality marine source rocks. The resulting speculation, it is reasonable to consider that there are high hydrocarbon generation potential source rocks in bathyal environment of the Qiongdongnan Basin, especially at the water depth 400-1 000 m.
Drilling wells reveal that the organic matter abundance of Miocene marine source rocks in shallow water area of the Qiongdongnan Basin is relatively low with poor hydrocarbon generation potential. However, in some drilling wells of deep water area close to the central depression belt, Miocene marine source rocks with better organic matter abundance and hydrocarbon generation have been found, which have achieved better source rock standard based on the analysis of geochemical characteristics. Although there are no exploratory wells in deep water area of the research region, through the comparative analysis of geochemical data of several typical exploratory wells respectively from shallow water area in the basin, central depression belt margin in deep-water area of the basin and Site 1148 of deep sea drilling in the South China Sea Basin, it reveals that the tendency of the quality of source rocks becomes positive gradually from delta to bathyal environment, which then becomes negative as in deep oceanic environment. Owing to the lack of terrestrial organic matter input, the important controlling factors of Miocene marine source rocks in the Qiongdongnan Basin are ocean productivity and preservation conditions of organic matter. The element geochemistry data indicate that the tendency of the paleoproductivity and the preservation conditions of organic matter become positive as water depth increase from shallow area to bathyal area close to central depression belt. So it is speculated that there must exist high quality source rocks in the central depression area where the preservation conditions of organic matter are much better. Besides, in theory, in oxygen-poor zone of oceanic environment at the water depth 400-1 000 m, the preservation conditions of organic matter are well thus forming high-quality marine source rocks. The resulting speculation, it is reasonable to consider that there are high hydrocarbon generation potential source rocks in bathyal environment of the Qiongdongnan Basin, especially at the water depth 400-1 000 m.
2012, (5): 115-125.
doi: 10.1007/s13131-012-0242-8
Abstract:
The study aims to compare the differences of macrofauna communities of wetlands at 3-year-forestage, 5-year-forest-age Sonneratia apetala artificial mangroves, 5-year-forest-age Kandelia candel artificial mangroves with the same restoration background, and the naked tidal flat in the Qi'ao Island Mangrove Nature Reserve of Zhuhai, Guangdong Province. The results show that there were significant structural differences in macrofauna communities among four kinds of habitats. The increase of biomass and species diversity of macrofauna at 3-year-forest-age S. apetala artificial mangroves was obviously faster than that at 5-year-forest-age K. candel artificial mangroves whose average tree height was close to that of 3-year-forest-age S. apetala artificial mangroves. The BIOENV analysis shows that it was related to the rapid growth of S. apetala, which rapidly changed the light level and shading conditions in the forests. The 5-year-forest-age S. apetala artificial mangroves had lower macrofauna species diversity but higher density and biomass than K. candel artificial mangroves with the same forest age. This was due to the rapid changes of physical and chemical properties of habitat soil by the ecological restoration of S. apetala artificial mangroves as well as the changed food sources possibly caused by the leaf-litter of such non-indigenous mangrove species S. apetala. However, further survey should be conducted on whether there are any negative ecological impacts of large-scale cultivation of S. apetala on macrofauna communities, so as to evaluate correctly S. apetala's role in the restoration of coastal mangrove ecosystems.
The study aims to compare the differences of macrofauna communities of wetlands at 3-year-forestage, 5-year-forest-age Sonneratia apetala artificial mangroves, 5-year-forest-age Kandelia candel artificial mangroves with the same restoration background, and the naked tidal flat in the Qi'ao Island Mangrove Nature Reserve of Zhuhai, Guangdong Province. The results show that there were significant structural differences in macrofauna communities among four kinds of habitats. The increase of biomass and species diversity of macrofauna at 3-year-forest-age S. apetala artificial mangroves was obviously faster than that at 5-year-forest-age K. candel artificial mangroves whose average tree height was close to that of 3-year-forest-age S. apetala artificial mangroves. The BIOENV analysis shows that it was related to the rapid growth of S. apetala, which rapidly changed the light level and shading conditions in the forests. The 5-year-forest-age S. apetala artificial mangroves had lower macrofauna species diversity but higher density and biomass than K. candel artificial mangroves with the same forest age. This was due to the rapid changes of physical and chemical properties of habitat soil by the ecological restoration of S. apetala artificial mangroves as well as the changed food sources possibly caused by the leaf-litter of such non-indigenous mangrove species S. apetala. However, further survey should be conducted on whether there are any negative ecological impacts of large-scale cultivation of S. apetala on macrofauna communities, so as to evaluate correctly S. apetala's role in the restoration of coastal mangrove ecosystems.
2012, (5): 126-134.
doi: 10.1007/s13131-012-0230-2
Abstract:
UV radiation is known to affect aquatic primary producers and their grazers. However, little has been documented on its effects on zooplankton grazing. In this study, the authors investigated the effects of photosynthetically active radiation (PAR, 400-700 nm), ultraviolet-A (UV-A, 320-400 nm) and ultraviolet-B (UV-B, 280-320 nm) radiation on grazing, mortality and lipids oxidation of the copepod Acartia pacifica collected from the Xiamen Bay. After 30 min of the exposures, the copepod was fed in darkness with the diatom Phaeodactylum tricornutum at two cell concentrations (2.5×104 and 2.5×105 cells/ml). At the low cell concentration, the individuals pre-exposed to PAR (218.0 W/m2)+UV-A (48.2 W/m2) or PAR+UV-A+UV-B (2.1 W/m2) showed suppressed clearance and grazing activities compared with those receiving PAR alone, by 22.7% and 17.1% for clearance and by 22.6% and 5.5% for grazing rates, respectively. However, the suppression on clearance and grazing became indistinctive at the high food concentration. Exposures to UV-A and UV-B led to increased lipid oxidation and higher mortality, furthermore, the mortality linearly increased with enhanced oxidation of lipid.
UV radiation is known to affect aquatic primary producers and their grazers. However, little has been documented on its effects on zooplankton grazing. In this study, the authors investigated the effects of photosynthetically active radiation (PAR, 400-700 nm), ultraviolet-A (UV-A, 320-400 nm) and ultraviolet-B (UV-B, 280-320 nm) radiation on grazing, mortality and lipids oxidation of the copepod Acartia pacifica collected from the Xiamen Bay. After 30 min of the exposures, the copepod was fed in darkness with the diatom Phaeodactylum tricornutum at two cell concentrations (2.5×104 and 2.5×105 cells/ml). At the low cell concentration, the individuals pre-exposed to PAR (218.0 W/m2)+UV-A (48.2 W/m2) or PAR+UV-A+UV-B (2.1 W/m2) showed suppressed clearance and grazing activities compared with those receiving PAR alone, by 22.7% and 17.1% for clearance and by 22.6% and 5.5% for grazing rates, respectively. However, the suppression on clearance and grazing became indistinctive at the high food concentration. Exposures to UV-A and UV-B led to increased lipid oxidation and higher mortality, furthermore, the mortality linearly increased with enhanced oxidation of lipid.
2012, (5): 135-145.
doi: 10.1007/s13131-012-0243-7
Abstract:
The potential suppression of copepods on appendicularians was found in field and experimental conditions. The abundance and distribution of appendicularians and planktonic copepods were studied with reference to their correlations during summer on the northwest continental shelf of the South China Sea (SCS). Based on the topography and water mass of the surveyed region, it was divided into three sub-regions:Region I (inshore waters of the east Leizhou Peninsula) with low temperature, salinity and high chlorophyll a (Chl a) concentration, Region Ⅱ (inshore waters of the east and southeast Hainan Island) with low temperature, high salinity and moderate Chl a concentration and Region Ⅲ (offshore waters from the Leizhou Peninsula to Hainan Island) with high temperature, high salinity and low Chl a concentration. The species richness of appendicularians and copepods increased from the inshore to offshore waters, and high values were observed in Region Ⅲ. The distribution of appendicularian and copepod abundance decreased generally from the inshore to offshore waters, with the highest values at Region I. Our results suggest that the distribution patterns of appendicularians and copepods differed significantly, as a result of the influence of physical and biological factors. The negative impact of pelagic copepods on appendicularians was not found based on in situ data in the northwest continental shelf of SCS.
The potential suppression of copepods on appendicularians was found in field and experimental conditions. The abundance and distribution of appendicularians and planktonic copepods were studied with reference to their correlations during summer on the northwest continental shelf of the South China Sea (SCS). Based on the topography and water mass of the surveyed region, it was divided into three sub-regions:Region I (inshore waters of the east Leizhou Peninsula) with low temperature, salinity and high chlorophyll a (Chl a) concentration, Region Ⅱ (inshore waters of the east and southeast Hainan Island) with low temperature, high salinity and moderate Chl a concentration and Region Ⅲ (offshore waters from the Leizhou Peninsula to Hainan Island) with high temperature, high salinity and low Chl a concentration. The species richness of appendicularians and copepods increased from the inshore to offshore waters, and high values were observed in Region Ⅲ. The distribution of appendicularian and copepod abundance decreased generally from the inshore to offshore waters, with the highest values at Region I. Our results suggest that the distribution patterns of appendicularians and copepods differed significantly, as a result of the influence of physical and biological factors. The negative impact of pelagic copepods on appendicularians was not found based on in situ data in the northwest continental shelf of SCS.
2012, (5): 146-159.
doi: 10.1007/s13131-012-0244-6
Abstract:
To study the effect of hydrographic factors on the spatial distributions of chlorophyll a (Chl a), an investigation was carried out in the tropical eastern Indian Ocean (80°-100°E along 7°S, and 7°-18°S along 80°E) in December 2010. The fluorescent method was used to obtain total Chl a and size-fractioned Chl a at the 26 stations. The results show that surface Chl a concentration averaged at (0.168±0.095) mg/m3 s.d. (range:0.034-0.475 mg/m3), concentrations appeared to be higher in the west for longitudinal variations, and higher in the north for latitudinal variations. Furthermore, the surface Chl a concentration was lower (0.034-0.066 mg/m3) in the region to the south of 16°S. There was a strong subsurface Chl a maximum layer at all stations and the depth of the Chl a maximum increased towards to the east and south along with the respective nitracline. The spatial variation of Chl a was significant:correlation and regression analysis suggests that it was primarily affected by PO43-, N(NO3-N+NO2-N) and temperature. Size-fractionated Chl a concentration clearly showed that the study area was a typical oligotrophic open ocean, in which picophytoplankton dominated, accounting for approximately 67.8% of total Chl a, followed by nanophytoplankton (24.5%) and microphytoplankton (7.6%). The two larger fractions were sensitive to the limitation of P, while picophytoplankton was primarily affected by temperature.
To study the effect of hydrographic factors on the spatial distributions of chlorophyll a (Chl a), an investigation was carried out in the tropical eastern Indian Ocean (80°-100°E along 7°S, and 7°-18°S along 80°E) in December 2010. The fluorescent method was used to obtain total Chl a and size-fractioned Chl a at the 26 stations. The results show that surface Chl a concentration averaged at (0.168±0.095) mg/m3 s.d. (range:0.034-0.475 mg/m3), concentrations appeared to be higher in the west for longitudinal variations, and higher in the north for latitudinal variations. Furthermore, the surface Chl a concentration was lower (0.034-0.066 mg/m3) in the region to the south of 16°S. There was a strong subsurface Chl a maximum layer at all stations and the depth of the Chl a maximum increased towards to the east and south along with the respective nitracline. The spatial variation of Chl a was significant:correlation and regression analysis suggests that it was primarily affected by PO43-, N(NO3-N+NO2-N) and temperature. Size-fractionated Chl a concentration clearly showed that the study area was a typical oligotrophic open ocean, in which picophytoplankton dominated, accounting for approximately 67.8% of total Chl a, followed by nanophytoplankton (24.5%) and microphytoplankton (7.6%). The two larger fractions were sensitive to the limitation of P, while picophytoplankton was primarily affected by temperature.
2012, (5): 160-164.
doi: 10.1007/s13131-012-0245-5
Abstract:
Harmonic analysis, the traditional tidal forecasting method, cannot take into account the impact of noncyclical factors, and is also based on the BP neural network tidal prediction model which is easily limited by the amount of data. According to the movement of celestial bodies, and considering the insufficient tidal characteristics of historical data which are impacted by the nonperiodic weather, a tidal prediction method is designed based on support vector machine (SVM) to carry out the simulation experiment by using tidal data from Xiamen Tide Gauge, Luchaogang Tide Gauge and Weifang Tide Gauge individually. And the results show that the model satisfactorily carries out the tide prediction which is influenced by noncyclical factors. At the same time, it also proves that the proposed prediction method, which when compared with harmonic analysis method and the BP neural network method, has faster modeling speed, higher prediction precision and stronger generalization ability.
Harmonic analysis, the traditional tidal forecasting method, cannot take into account the impact of noncyclical factors, and is also based on the BP neural network tidal prediction model which is easily limited by the amount of data. According to the movement of celestial bodies, and considering the insufficient tidal characteristics of historical data which are impacted by the nonperiodic weather, a tidal prediction method is designed based on support vector machine (SVM) to carry out the simulation experiment by using tidal data from Xiamen Tide Gauge, Luchaogang Tide Gauge and Weifang Tide Gauge individually. And the results show that the model satisfactorily carries out the tide prediction which is influenced by noncyclical factors. At the same time, it also proves that the proposed prediction method, which when compared with harmonic analysis method and the BP neural network method, has faster modeling speed, higher prediction precision and stronger generalization ability.
2012, (5): 165-175.
doi: 10.1007/s13131-012-0246-4
Abstract:
The spatial variations of phytoplankton community structure in the Xiamen Western Bay during the summer and autumn cruises in 2001 were investigated based on HPLC analysis of photosynthetic pigments in algal cells and CHEMTAX processing of pigment data. The Chl a concentration reached 18.9 μg/L in the summer and declined to 0.28-2.17 in the autumn, respectively, consistent with the observation of diatom blooms in June. Among the accessory pigments, fucoxanthin was consistently the most abundant, ranging from 0.172 to 8.46 μg/L, with the maximum concentrations in June. 19'-hexfucoxanthin and alloxanthin were the other two abundant pigments in the summer and autumn. In addition, 19'-butanoyloxyfucoxanthin or peridinin was also important in late autumn. Generally the biomass of all the phytoplankton or each group was higher in the inner part than the mouth of this bay, represented by Chl a. CHEMTAX processing revealed the dominance of diatoms with their contribution of 14.6%-52.5% to the total Chl a, but its importance decreased in the autumn. Cryptophytes and Haptophytes, with an average contribution of 16.9%-31.4% and 12.1%-26.3%, were the other two important groups, especially in the autumn. On the contrary, Dinoflagellates and Chlorophytes were the minor groups, but the former became important sporadically in the autumn. It was suggested that there was distinctive variation in both the phytoplankton community structure and biomass between summer and autumn in the Xiamen Western Bay and the latter was coupled to the changes in temperature and dissolved oxygen. However, the spatial variation of the phytoplankton community structure was not as clear as the trend in the biomass of phytoplankton among all the sites in this bay.
The spatial variations of phytoplankton community structure in the Xiamen Western Bay during the summer and autumn cruises in 2001 were investigated based on HPLC analysis of photosynthetic pigments in algal cells and CHEMTAX processing of pigment data. The Chl a concentration reached 18.9 μg/L in the summer and declined to 0.28-2.17 in the autumn, respectively, consistent with the observation of diatom blooms in June. Among the accessory pigments, fucoxanthin was consistently the most abundant, ranging from 0.172 to 8.46 μg/L, with the maximum concentrations in June. 19'-hexfucoxanthin and alloxanthin were the other two abundant pigments in the summer and autumn. In addition, 19'-butanoyloxyfucoxanthin or peridinin was also important in late autumn. Generally the biomass of all the phytoplankton or each group was higher in the inner part than the mouth of this bay, represented by Chl a. CHEMTAX processing revealed the dominance of diatoms with their contribution of 14.6%-52.5% to the total Chl a, but its importance decreased in the autumn. Cryptophytes and Haptophytes, with an average contribution of 16.9%-31.4% and 12.1%-26.3%, were the other two important groups, especially in the autumn. On the contrary, Dinoflagellates and Chlorophytes were the minor groups, but the former became important sporadically in the autumn. It was suggested that there was distinctive variation in both the phytoplankton community structure and biomass between summer and autumn in the Xiamen Western Bay and the latter was coupled to the changes in temperature and dissolved oxygen. However, the spatial variation of the phytoplankton community structure was not as clear as the trend in the biomass of phytoplankton among all the sites in this bay.
