2022 Vol. 44, No. 9
Display Method:
2022, 44(9): 1-12.
doi: 10.12284/hyxb2022107
Abstract:
Fe is the most abundant variable-valence element in igneous rocks, and is also an important mineralizing element, mainly in the solid (mineral) and liquid (fluid) phases in Fe2+ or Fe3+ valence state, and participates in magmatic processes and various mineralization throughout. With the development of test analytical techniques (e.g. MC-ICPMS), the analysis of non-traditional stable isotope compositions such as Fe has become possible and has been successfully applied to the study of important geological processes such as magma source tracing, tracing of crystallization evolutionary processes and mineralization analysis in the last decade or so. Based on the analysis of the fractionation effect of Fe isotopes during magmatism, this paper summarized the latest results of Fe isotope composition studies in tracing the action of seafloor basaltic magmas (MORB, OIB, IAB and BABB, etc.) and discussed the main problems in the application of Fe isotope composition in tracing the action of seafloor magmas. The results of the comprehensive analysis show that the Fe isotope fractionation effect in igneous rocks is influenced not only by the processes of partial melting of magma source material, magma diffusion, fluid exsolution and crystallization differentiation, but also by the assimilation of surrounding rock material and seafloor alteration. Since Fe isotope analysis techniques (methods) have yet to be further refined, and the available data are limited and need to be screened for artifacts, caution is still needed when using Fe isotope compositions to analyze or recover magmatic sources and processes. It is urgent to establish a complete and reliable Fe isotope tracing system, which requires the recent work to select as many suitable samples as possible representing different tectonic environments and different rock types, to obtain (accumulate) more fine analytical data of original (unmodified or altered) samples, and to pay attention to the combination or mutual corroboration of multiple data in the process of using Fe isotope tracing for seafloor magmatism.
Fe is the most abundant variable-valence element in igneous rocks, and is also an important mineralizing element, mainly in the solid (mineral) and liquid (fluid) phases in Fe2+ or Fe3+ valence state, and participates in magmatic processes and various mineralization throughout. With the development of test analytical techniques (e.g. MC-ICPMS), the analysis of non-traditional stable isotope compositions such as Fe has become possible and has been successfully applied to the study of important geological processes such as magma source tracing, tracing of crystallization evolutionary processes and mineralization analysis in the last decade or so. Based on the analysis of the fractionation effect of Fe isotopes during magmatism, this paper summarized the latest results of Fe isotope composition studies in tracing the action of seafloor basaltic magmas (MORB, OIB, IAB and BABB, etc.) and discussed the main problems in the application of Fe isotope composition in tracing the action of seafloor magmas. The results of the comprehensive analysis show that the Fe isotope fractionation effect in igneous rocks is influenced not only by the processes of partial melting of magma source material, magma diffusion, fluid exsolution and crystallization differentiation, but also by the assimilation of surrounding rock material and seafloor alteration. Since Fe isotope analysis techniques (methods) have yet to be further refined, and the available data are limited and need to be screened for artifacts, caution is still needed when using Fe isotope compositions to analyze or recover magmatic sources and processes. It is urgent to establish a complete and reliable Fe isotope tracing system, which requires the recent work to select as many suitable samples as possible representing different tectonic environments and different rock types, to obtain (accumulate) more fine analytical data of original (unmodified or altered) samples, and to pay attention to the combination or mutual corroboration of multiple data in the process of using Fe isotope tracing for seafloor magmatism.
2022, 44(9): 73-86.
doi: 10.12284/hyxb2022071
Abstract:
In recent years, the topography of Huanghe River Delta exhibits significant changes due to natural and man-made reasons, such as delta acceleration and dyke construction. At the same time, these factors also lead to important variations in the tidal wave system and material transport path in the adjacent sea area. In this study, we establish a three-dimensional high-resolution tide, current and Lagrangian particle tracking numerical model of the Huanghe River Delta and its adjacent sea area based on FVCOM. Our modeling results agree well with the tidal harmonic constant of the tide gauge stations in Bohai Sea region and the observation data of tide level stations and current stations in the Huanghe River Delta. Thus, this model can reflect the characteristics of tide and tidal current in the Huanghe River Delta and its adjacent sea area. Furthermore, the location of the 2019 amphidromic point of M2 is also obtained from this model. By designing five numerical experiments of natural coastline evolution, dyke construction and corresponding water depth changes in the Huanghe River Delta in 1980 and 2019, the following conclusions are drawn. Firstly, from 1980 to 2019, the amphidromic point of M2 moves southeast, with the major factor of water depth. Secondly, changes of coastal line caused by the extension of the Huanghe River Estuary and the construction of dykes have minor effects to the location of amphidromic point of M2. Nevertheless, these changes can form the residual current gyres on both sides of the convex bank. As a result, the material from the Huanghe River stays longer in Laizhou Bay and delays its transportation and diffusion to Bohai Sea.
In recent years, the topography of Huanghe River Delta exhibits significant changes due to natural and man-made reasons, such as delta acceleration and dyke construction. At the same time, these factors also lead to important variations in the tidal wave system and material transport path in the adjacent sea area. In this study, we establish a three-dimensional high-resolution tide, current and Lagrangian particle tracking numerical model of the Huanghe River Delta and its adjacent sea area based on FVCOM. Our modeling results agree well with the tidal harmonic constant of the tide gauge stations in Bohai Sea region and the observation data of tide level stations and current stations in the Huanghe River Delta. Thus, this model can reflect the characteristics of tide and tidal current in the Huanghe River Delta and its adjacent sea area. Furthermore, the location of the 2019 amphidromic point of M2 is also obtained from this model. By designing five numerical experiments of natural coastline evolution, dyke construction and corresponding water depth changes in the Huanghe River Delta in 1980 and 2019, the following conclusions are drawn. Firstly, from 1980 to 2019, the amphidromic point of M2 moves southeast, with the major factor of water depth. Secondly, changes of coastal line caused by the extension of the Huanghe River Estuary and the construction of dykes have minor effects to the location of amphidromic point of M2. Nevertheless, these changes can form the residual current gyres on both sides of the convex bank. As a result, the material from the Huanghe River stays longer in Laizhou Bay and delays its transportation and diffusion to Bohai Sea.
2022, 44(9): 87-99.
doi: 10.12284/hyxb2022067
Abstract:
We deals with the tectonic evolution of the Andaman Sea, the northeastern margin of the Indian Ocean. Based on large-scale 2D seismic data and drilling data in the eastern Andaman Sea area, combined with regional geological survey and previous research results, eight representative faults were selected and divided into first-order and second-order faults. Growth index method and paleo-fall method were used to quantitatively analyze the faults. The tectonic evolution of the eastern Andaman Sea depression is discussed by calculating the tectonic subsidence of the four main survey lines. The results show that three of the selected growth faults are first-level faults with large span and almost cut through the whole stratum, which are large faults controlling the subsidence of the Andaman Sea area. The other five are secondary faults, controlling the distribution of the tectonic belt and belonging to the boundary of the tectonic belt. During the Oligocene, the Indo-Australian Plate and Eurasian Plate were in the stage of soft collision, with slow fault development, small overhanging and footrow drop, low growth index and tectonic subsidence. During the Miocene, the coupling effect between plates was strengthened, the fault development speed was accelerated, and the thickness of the upper and lower walls was the largest. It was the key period for the formation of multiple fault zones and various fault styles, and the growth index of various layers and the tectonic subsidence reached the peak. Since the Pliocene, the Andaman trench-arc-basin system has gradually stabilized, the fault activity has weakened, the thickness difference between the upper and lower wall of the fault is basically the same, the growth index difference is small, and the tectonic subsidence is basically stable at about 1 km.
We deals with the tectonic evolution of the Andaman Sea, the northeastern margin of the Indian Ocean. Based on large-scale 2D seismic data and drilling data in the eastern Andaman Sea area, combined with regional geological survey and previous research results, eight representative faults were selected and divided into first-order and second-order faults. Growth index method and paleo-fall method were used to quantitatively analyze the faults. The tectonic evolution of the eastern Andaman Sea depression is discussed by calculating the tectonic subsidence of the four main survey lines. The results show that three of the selected growth faults are first-level faults with large span and almost cut through the whole stratum, which are large faults controlling the subsidence of the Andaman Sea area. The other five are secondary faults, controlling the distribution of the tectonic belt and belonging to the boundary of the tectonic belt. During the Oligocene, the Indo-Australian Plate and Eurasian Plate were in the stage of soft collision, with slow fault development, small overhanging and footrow drop, low growth index and tectonic subsidence. During the Miocene, the coupling effect between plates was strengthened, the fault development speed was accelerated, and the thickness of the upper and lower walls was the largest. It was the key period for the formation of multiple fault zones and various fault styles, and the growth index of various layers and the tectonic subsidence reached the peak. Since the Pliocene, the Andaman trench-arc-basin system has gradually stabilized, the fault activity has weakened, the thickness difference between the upper and lower wall of the fault is basically the same, the growth index difference is small, and the tectonic subsidence is basically stable at about 1 km.
2022, 44(9): 100-108.
doi: 10.12284/hyxb2022111
Abstract:
The hard-thin layers (HTLs) are usually composed of submerged coral reefs, various cemented sands, cemented coral stones or shell fragments and their locations are difficult to be determined by geological sampling due to their sporadic distribution. They bring great challenges and risks to the construction of submarine pipelines. In this paper, taking the northern shelf of the South China Sea as an example, we summarized the acoustic characteristics of the HTLs on the seabed and in the shallow sediments based on a variety of high-resolution geophysical data combined with forward simulation analysis. Twenty-three areas with HTLs in the study area were determined. Our study suggests that differences in the physical properties of HTLs and loose sediments help identify and locate them using high-resolution geophysical data. On the sub-bottom profiles, the HTLs are characterized by reflective interfaces with high-amplitude, beneath of which the low-amplitude reflections usually occur. These reflection features help to determine the HTLs, their depths and locations. The HTLs usually display the alternating light and dark zones with irregular boundaries on the side scan sonar and backscatter intensity images. When the HTLs are located on the seafloor, the comprehensive interpretation of the side-scan images, backscatter intensity images and the sub-bottom profiles is effective to identify and locate them. For those THLs several meters to ten meters below the seafloor, high-resolution sub-bottom profiles may be the only and most effective way to identify and locate them.
The hard-thin layers (HTLs) are usually composed of submerged coral reefs, various cemented sands, cemented coral stones or shell fragments and their locations are difficult to be determined by geological sampling due to their sporadic distribution. They bring great challenges and risks to the construction of submarine pipelines. In this paper, taking the northern shelf of the South China Sea as an example, we summarized the acoustic characteristics of the HTLs on the seabed and in the shallow sediments based on a variety of high-resolution geophysical data combined with forward simulation analysis. Twenty-three areas with HTLs in the study area were determined. Our study suggests that differences in the physical properties of HTLs and loose sediments help identify and locate them using high-resolution geophysical data. On the sub-bottom profiles, the HTLs are characterized by reflective interfaces with high-amplitude, beneath of which the low-amplitude reflections usually occur. These reflection features help to determine the HTLs, their depths and locations. The HTLs usually display the alternating light and dark zones with irregular boundaries on the side scan sonar and backscatter intensity images. When the HTLs are located on the seafloor, the comprehensive interpretation of the side-scan images, backscatter intensity images and the sub-bottom profiles is effective to identify and locate them. For those THLs several meters to ten meters below the seafloor, high-resolution sub-bottom profiles may be the only and most effective way to identify and locate them.
2022, 44(9): 109-123.
doi: 10.12284/hyxb2022065
Abstract:
Reconstruction of high-quality Holocene relative sea levels (RSL) based on geological records can provide important past analogue and long-term reference for coastal societies to make better prediction and preparation for future sea-level rise. In the last decades, several Holocene RSL curves have already been published from Fujian coast, southeastern China. However, obvious differences and even contradictory results existed in these early-stage researches. At the same time, the mechanism and factors which control the long-term RSL change in this area are also unclear. In this study, new and published RSL data have been compiled from Fujian coast. Attribute information including location, age, elevation and indicative meaning of each data point has been re-examined and corrected. After that, a standardized Holocene relative sea level database which includes a total number of 183 data were established. On this basis, a new regional Holocene RSL curve was proposed by using the errors in variable-integrated gaussian process (EIV-IGP) statistical model. Finally, theoretical RSL change was predicted through solving the sea level equation (SLE). Combining the RSL geological records and GIA simulation results, conclusions are drawn as follow: (1) New Holocene RSL history of Fujian coast was reconstructed. 11.28–7.08 cal ka before present, RSL rose from (–23.55±6.94) m to (–1.51±1.80) m continuously; 7.08–4.08 cal ka before present, RSL rose slowly from (–1.51±1.80) m to (1.09 ±1.38) m; around 3.48 cal ka before present, RSL was about (1.35±1.23) m higher than modern sea level. Since then, the RSL has declined close to the modern position gradually. (2) In the Early Holocene (11.28–7.00 cal ka before present), the RSL change was mainly controlled by the meltwater from continental ice-sheet; and since 7.00 cal ka before present, hydro-isostatic process dominated the regional RSL change. (3) Holocene sea level highstand existed during 6.75–0.16 cal ka before present on Fujian coast. The highstand of sea level could be attributed to continental levering and ocean syphoning processes caused by GIA rather than tectonic movement. (4) Holocene RSL change showed spatial variability on the Fujian coast. Non-GIA factors including the compaction of unconsolidated strata, differential tectonic movements and tidal range changes, supposed to be related to this phenomenon.
Reconstruction of high-quality Holocene relative sea levels (RSL) based on geological records can provide important past analogue and long-term reference for coastal societies to make better prediction and preparation for future sea-level rise. In the last decades, several Holocene RSL curves have already been published from Fujian coast, southeastern China. However, obvious differences and even contradictory results existed in these early-stage researches. At the same time, the mechanism and factors which control the long-term RSL change in this area are also unclear. In this study, new and published RSL data have been compiled from Fujian coast. Attribute information including location, age, elevation and indicative meaning of each data point has been re-examined and corrected. After that, a standardized Holocene relative sea level database which includes a total number of 183 data were established. On this basis, a new regional Holocene RSL curve was proposed by using the errors in variable-integrated gaussian process (EIV-IGP) statistical model. Finally, theoretical RSL change was predicted through solving the sea level equation (SLE). Combining the RSL geological records and GIA simulation results, conclusions are drawn as follow: (1) New Holocene RSL history of Fujian coast was reconstructed. 11.28–7.08 cal ka before present, RSL rose from (–23.55±6.94) m to (–1.51±1.80) m continuously; 7.08–4.08 cal ka before present, RSL rose slowly from (–1.51±1.80) m to (1.09 ±1.38) m; around 3.48 cal ka before present, RSL was about (1.35±1.23) m higher than modern sea level. Since then, the RSL has declined close to the modern position gradually. (2) In the Early Holocene (11.28–7.00 cal ka before present), the RSL change was mainly controlled by the meltwater from continental ice-sheet; and since 7.00 cal ka before present, hydro-isostatic process dominated the regional RSL change. (3) Holocene sea level highstand existed during 6.75–0.16 cal ka before present on Fujian coast. The highstand of sea level could be attributed to continental levering and ocean syphoning processes caused by GIA rather than tectonic movement. (4) Holocene RSL change showed spatial variability on the Fujian coast. Non-GIA factors including the compaction of unconsolidated strata, differential tectonic movements and tidal range changes, supposed to be related to this phenomenon.
2022, 44(9): 156-164.
doi: 10.12284/hyxb2022113
Abstract:
The physical properties of seafloor sediments (less than 1 m), such as particle size, porosity and density, are an important part of marine sedimental research and marine engineering geological analysis. The acquisition of these physical properties is currently based on limited seabed sampling or in-situ testing. The sub-bottom profile is based on the propagation of acoustic signals (frequencies in thousands of Hertz) in sediments to obtain the data that can reflect the sedimentary stratigraphic structure. Some of the acoustic parameters, such as seabed reflection coefficient and wave impedance, are closely related to the physical properties of sediments. How to make full and effective use of the sub-bottom profile data to retrieve the physical property parameters of the seafloor sediments in the profile overlying area is of great scientific significance and application value. Moreover, inversion of the physical properties of sediments based on acoustic properties is a hot research topic at present. Therefore, in this paper, the Biot-Stoll model is used to establish the relationship between the seabed reflection coefficient and the physical properties of the sediments in the study area based on the measured physical parameters of the seafloor sediments from LD 16-3CEPA to LD10-1PAPD routing section of the Bohai Sea. Based on the seabed reflection coefficient calculated from the sub-bottom profile data, the physical property parameters such as porosity, density and mean grain size of the seabed sediment in the study area are retrieved. The porosity, density and mean grain size of the inversion are basically consistent with the measured, and the deviation degree is basically within the range of 20%, indicating that the application of the inversion method in this area is feasible.
The physical properties of seafloor sediments (less than 1 m), such as particle size, porosity and density, are an important part of marine sedimental research and marine engineering geological analysis. The acquisition of these physical properties is currently based on limited seabed sampling or in-situ testing. The sub-bottom profile is based on the propagation of acoustic signals (frequencies in thousands of Hertz) in sediments to obtain the data that can reflect the sedimentary stratigraphic structure. Some of the acoustic parameters, such as seabed reflection coefficient and wave impedance, are closely related to the physical properties of sediments. How to make full and effective use of the sub-bottom profile data to retrieve the physical property parameters of the seafloor sediments in the profile overlying area is of great scientific significance and application value. Moreover, inversion of the physical properties of sediments based on acoustic properties is a hot research topic at present. Therefore, in this paper, the Biot-Stoll model is used to establish the relationship between the seabed reflection coefficient and the physical properties of the sediments in the study area based on the measured physical parameters of the seafloor sediments from LD 16-3CEPA to LD10-1PAPD routing section of the Bohai Sea. Based on the seabed reflection coefficient calculated from the sub-bottom profile data, the physical property parameters such as porosity, density and mean grain size of the seabed sediment in the study area are retrieved. The porosity, density and mean grain size of the inversion are basically consistent with the measured, and the deviation degree is basically within the range of 20%, indicating that the application of the inversion method in this area is feasible.
2022, 44(9): 13-22.
doi: 10.12284/hyxb2022099
Abstract:
The Atlantic meridional overturning circulation (AMOC) is an important component of the climate system, of which change in the strength can affect meridional heat distribution between the northern and southern hemispheres. Proxy records show that changes in Atlantic Ocean circulation during the Late Pleistocene is associated with precessional cycle, but its physical mechanism remains unclear. Here we use a fully coupled climate model to investigate dynamics associated with AMOC changes in precessional band under glacial-interglacial climate conditions. Our results show that increase in boreal summer insolation can effectively weaken the AMOC during warm interglacial periods, while this weakening effect is reduced under glacial maximum. We further demonstrate that during the warm interglacial period increase in boreal summer insolation leads to sea surface warming and subpolar rainfall increase in North Atlantic, which jointly reduces sea surface density and hence the strength of deep water formation. During the glacial maximum period, climate responses to precessional change is of anti-phase impacts on the AMOC. At the low latitudes, a low pressure anomaly triggered by subtropical warming weakens atmospheric moisture export from the subtropical Atlantic to Pacific, increasing in net precipitation and hence freshening tropical sea surface in the North Atlantic. At the high latitudes, the warming-induced sea ice retreat promotes ocean heat loss via the enlarged ice-free area, and hence tends to strengthen the vertical mixing. The combined effects of low- and high-latitude responses finally leads to a trivial weakening of the AMOC. Overall, our results provide a systematic understanding of governing mechanism for precessionally-induced AMOC change under glacial-interglacial climatic backgrounds, shedding light on our interpretation of precessional periodicity in reconstructed ocean circulation changes during the Pleistocene.
The Atlantic meridional overturning circulation (AMOC) is an important component of the climate system, of which change in the strength can affect meridional heat distribution between the northern and southern hemispheres. Proxy records show that changes in Atlantic Ocean circulation during the Late Pleistocene is associated with precessional cycle, but its physical mechanism remains unclear. Here we use a fully coupled climate model to investigate dynamics associated with AMOC changes in precessional band under glacial-interglacial climate conditions. Our results show that increase in boreal summer insolation can effectively weaken the AMOC during warm interglacial periods, while this weakening effect is reduced under glacial maximum. We further demonstrate that during the warm interglacial period increase in boreal summer insolation leads to sea surface warming and subpolar rainfall increase in North Atlantic, which jointly reduces sea surface density and hence the strength of deep water formation. During the glacial maximum period, climate responses to precessional change is of anti-phase impacts on the AMOC. At the low latitudes, a low pressure anomaly triggered by subtropical warming weakens atmospheric moisture export from the subtropical Atlantic to Pacific, increasing in net precipitation and hence freshening tropical sea surface in the North Atlantic. At the high latitudes, the warming-induced sea ice retreat promotes ocean heat loss via the enlarged ice-free area, and hence tends to strengthen the vertical mixing. The combined effects of low- and high-latitude responses finally leads to a trivial weakening of the AMOC. Overall, our results provide a systematic understanding of governing mechanism for precessionally-induced AMOC change under glacial-interglacial climatic backgrounds, shedding light on our interpretation of precessional periodicity in reconstructed ocean circulation changes during the Pleistocene.
2022, 44(9): 23-37.
doi: 10.12284/hyxb2022109
Abstract:
This study utilizes a new functional analysis tool, multiscale window transform (MWT), to decompose the ocean circulation system in the Bay of Bengal (BOB) into three scale windows, namely, the background flow window (>96 days), the mesoscale window (24–96 days) and the high-frequency window (<24 days), and then uses the canonical energy transfer theory to investigate the intrinsic nonlinear multiscale interactions among these windows, on the basis of an eddy-resolving model simulation. It is found that multiscale interactions are strongest along the northwestern boundary and east of Sri Lanka. With intense barotropic and baroclinic instabilities, the canonical transfers of kinetic energy (KE) and available potential energy (APE) are mainly forward in these two regions. Mesoscale eddy kinetic energy (EKE) reservoir is mainly filled by the barotropic energy pathway with the kinetic energy of the background flow transferring to EKE, and secondarily from the baroclinic energy pathway with APE of the background flow transferring to the mesoscale APE and further converting to EKE. The gained EKE is found to further cascade to high-frequency motions, acting as an important dissipation mechanism of the mesoscale eddies in these regions. In contrast, the central BOB is mainly characterized by inverse KE cascades, where EKE and high-frequency kinetic energy (HKE) are gained via the baroclinic energy pathway, and then feed the background flow through inverse cascade processes. The northwest of Sumatra is also an area with strong mesoscale and high-frequency variability. Both barotropic and baroclinic energy pathways are the sources for EKE and HKE reservoirs in this region, with the baroclinic energy pathway playing the dominant role.
This study utilizes a new functional analysis tool, multiscale window transform (MWT), to decompose the ocean circulation system in the Bay of Bengal (BOB) into three scale windows, namely, the background flow window (>96 days), the mesoscale window (24–96 days) and the high-frequency window (<24 days), and then uses the canonical energy transfer theory to investigate the intrinsic nonlinear multiscale interactions among these windows, on the basis of an eddy-resolving model simulation. It is found that multiscale interactions are strongest along the northwestern boundary and east of Sri Lanka. With intense barotropic and baroclinic instabilities, the canonical transfers of kinetic energy (KE) and available potential energy (APE) are mainly forward in these two regions. Mesoscale eddy kinetic energy (EKE) reservoir is mainly filled by the barotropic energy pathway with the kinetic energy of the background flow transferring to EKE, and secondarily from the baroclinic energy pathway with APE of the background flow transferring to the mesoscale APE and further converting to EKE. The gained EKE is found to further cascade to high-frequency motions, acting as an important dissipation mechanism of the mesoscale eddies in these regions. In contrast, the central BOB is mainly characterized by inverse KE cascades, where EKE and high-frequency kinetic energy (HKE) are gained via the baroclinic energy pathway, and then feed the background flow through inverse cascade processes. The northwest of Sumatra is also an area with strong mesoscale and high-frequency variability. Both barotropic and baroclinic energy pathways are the sources for EKE and HKE reservoirs in this region, with the baroclinic energy pathway playing the dominant role.
2022, 44(9): 38-54.
doi: 10.12284/hyxb2022069
Abstract:
Previous studies have shown that the decadal modulation of the Kuroshio extension (KE) system is controlled by the Pacific decadal oscillation-associated forcing from downstream. However, recent observation reveals that this mechanism ceases to function after August 2017. Meanwhile, a large meander is under development in the KE’s upstream, i.e., south of Japan. Using the self-organizing map (SOM), we investigate the characteristic spatial and temporal patterns of the Kuroshio south of Japan and the KE and their causal relations, based on the 26-year (1993−2018) satellite altimetry data of sea level anomaly (SLA). The typical spatial patterns are well extracted, and their temporal trajectories indicate that the KE tends to be stable (unstable) when the upstream Kuroshio takes a large meander (an offshore nonlarge meander) path. To further unravel the underlying cause-and-effect relation between the two systems, we apply the information flow-based causality analysis to the typical regions of SLA and its associated temporal modes identified with the SOM. It is found that during the large meander event, the Kuroshio south of Japan and the KE are mutually causal, but have different hotspots. The information flows from the former to the latter mainly occur in the southeastern area off the Kii Peninsula and the time-mean ridge and trough of the KE jet, while those from the latter to the former are mainly concentrated in the time-mean ridge and trough of the KE jet, and the recirculation gyre of the Kuroshio. These results indicate that the Kuroshio large meander is an important factor influencing the KE’s stability, while the KE affects its upstream Kuroshio via modulating the associated recirculation gyres. In contrast, when the offshore nonlarge meander path is taken, a one-way causality is identified from the Kuroshio to the KE, mainly occurring over the Izu-Ogasawara Ridge and in the recirculation gyres. This may be attributed to the constantly downstream transport of negative SLAs into the KE’s recirculation gyre, which leads to an unstable KE.
Previous studies have shown that the decadal modulation of the Kuroshio extension (KE) system is controlled by the Pacific decadal oscillation-associated forcing from downstream. However, recent observation reveals that this mechanism ceases to function after August 2017. Meanwhile, a large meander is under development in the KE’s upstream, i.e., south of Japan. Using the self-organizing map (SOM), we investigate the characteristic spatial and temporal patterns of the Kuroshio south of Japan and the KE and their causal relations, based on the 26-year (1993−2018) satellite altimetry data of sea level anomaly (SLA). The typical spatial patterns are well extracted, and their temporal trajectories indicate that the KE tends to be stable (unstable) when the upstream Kuroshio takes a large meander (an offshore nonlarge meander) path. To further unravel the underlying cause-and-effect relation between the two systems, we apply the information flow-based causality analysis to the typical regions of SLA and its associated temporal modes identified with the SOM. It is found that during the large meander event, the Kuroshio south of Japan and the KE are mutually causal, but have different hotspots. The information flows from the former to the latter mainly occur in the southeastern area off the Kii Peninsula and the time-mean ridge and trough of the KE jet, while those from the latter to the former are mainly concentrated in the time-mean ridge and trough of the KE jet, and the recirculation gyre of the Kuroshio. These results indicate that the Kuroshio large meander is an important factor influencing the KE’s stability, while the KE affects its upstream Kuroshio via modulating the associated recirculation gyres. In contrast, when the offshore nonlarge meander path is taken, a one-way causality is identified from the Kuroshio to the KE, mainly occurring over the Izu-Ogasawara Ridge and in the recirculation gyres. This may be attributed to the constantly downstream transport of negative SLAs into the KE’s recirculation gyre, which leads to an unstable KE.
2022, 44(9): 55-62.
doi: 10.12284/hyxb2022119
Abstract:
Based on the 29-day full-depth mooring data of coral reef lagoon of Xisha Islands in South China Sea, we investigated the characteristics of the internal tides (ITs), the applicability of depth-averaging method for current analysis, and the source of ITs. The depth-averaged currents indicated that the diurnal tides were dominant, their HKE (horizontal kinetic energy) accounted for 41% of the total currents. The harmonic analyses of depth-averaged current and Tpxo7.2 model current indicated that the barotropic diurnal currents were modulated by topography, its main axis orientation was northwest-southeast. The spring-neap periods of barotropic diurnal currents with two methods have the half-phase shift (6−7 days). It is proposed that the depth-averaged barotropic diurnal currents contain the baroclinic diurnal components (diurnal internal tides) due to the lacking of measurements near the surface and bottom ocean. Further analysis showed that the barotropic and baroclinic diurnal currents had different amplitudes with the variable phase shift. The coherent diurnal ITs contributed 91% HKE to the total diurnal ITs, which implied that ITs was most generated in Xisha Islands.
Based on the 29-day full-depth mooring data of coral reef lagoon of Xisha Islands in South China Sea, we investigated the characteristics of the internal tides (ITs), the applicability of depth-averaging method for current analysis, and the source of ITs. The depth-averaged currents indicated that the diurnal tides were dominant, their HKE (horizontal kinetic energy) accounted for 41% of the total currents. The harmonic analyses of depth-averaged current and Tpxo7.2 model current indicated that the barotropic diurnal currents were modulated by topography, its main axis orientation was northwest-southeast. The spring-neap periods of barotropic diurnal currents with two methods have the half-phase shift (6−7 days). It is proposed that the depth-averaged barotropic diurnal currents contain the baroclinic diurnal components (diurnal internal tides) due to the lacking of measurements near the surface and bottom ocean. Further analysis showed that the barotropic and baroclinic diurnal currents had different amplitudes with the variable phase shift. The coherent diurnal ITs contributed 91% HKE to the total diurnal ITs, which implied that ITs was most generated in Xisha Islands.
2022, 44(9): 145-155.
doi: 10.12284/hyxb2022091
Abstract:
To accurately establish a geoacoustic model for seafloor sediments, the elemental composition and structure of the geoacoustic model are explored in this paper. Based on the laboratory measurements of seafloor sediment samples, the buried depth relationship between density, porosity, and sound velocity of seafloor surface sediments in the South China Sea is analyzed. Four typical seafloor geoacoustic structures are obtained: low sound velocity surface-sound velocity slow change type, low sound velocity surface-sound velocity increase type, high sound velocity surface-sound velocity slow change type, and high sound velocity surface-sound velocity increase type. By comparing the drilling survey and analyzing the buried depth relationship between density, porosity, and sound velocity of seafloor sediments in the Yellow Sea, the actual layered characteristics and the combination characteristics of the geoacoustic structure are obtained. It shows that the geoacoustic model can be attributed to a combination of four basic geoacoustic structures. Various actual seafloor geoacoustic models can be derived from the comparisons between the acoustic sound speed of the bottom seawater, the sound velocity profile of seafloor sediments in the same layer, and the bottom sound velocity of the upper sediment. The geoacoustic model based on the laboratory measurement analysis of seafloor sediment samples can be used as a reference geoacoustic model. However, it should be modified with the sound velocity ratio correction method and theoretical calculation method of dispersion characteristics with the consideration of the actual seafloor temperature gradient, pressure gradient, and dispersion characteristics of seafloor sediment.
To accurately establish a geoacoustic model for seafloor sediments, the elemental composition and structure of the geoacoustic model are explored in this paper. Based on the laboratory measurements of seafloor sediment samples, the buried depth relationship between density, porosity, and sound velocity of seafloor surface sediments in the South China Sea is analyzed. Four typical seafloor geoacoustic structures are obtained: low sound velocity surface-sound velocity slow change type, low sound velocity surface-sound velocity increase type, high sound velocity surface-sound velocity slow change type, and high sound velocity surface-sound velocity increase type. By comparing the drilling survey and analyzing the buried depth relationship between density, porosity, and sound velocity of seafloor sediments in the Yellow Sea, the actual layered characteristics and the combination characteristics of the geoacoustic structure are obtained. It shows that the geoacoustic model can be attributed to a combination of four basic geoacoustic structures. Various actual seafloor geoacoustic models can be derived from the comparisons between the acoustic sound speed of the bottom seawater, the sound velocity profile of seafloor sediments in the same layer, and the bottom sound velocity of the upper sediment. The geoacoustic model based on the laboratory measurement analysis of seafloor sediment samples can be used as a reference geoacoustic model. However, it should be modified with the sound velocity ratio correction method and theoretical calculation method of dispersion characteristics with the consideration of the actual seafloor temperature gradient, pressure gradient, and dispersion characteristics of seafloor sediment.
2022, 44(9): 63-72.
doi: 10.12284/hyxb2022073
Abstract:
Atmospheric deposition is the most important source for 210Po, 210Bi, 210Pb and 7Be radionuclides in the Arctic sea ice regions far away from the influence of rivers and continents. Once the precipitation or snow forms in the Arctic, the falling snow underneath the cloud would be tagged with the specific 210Po/210Pb activity ratio and be locked into a closed environment; as time elapses, this ratio in snow increases to equilibrium state of 210Po-210Pb due to 210Po ingrowth from the decay of 210Pb. From the measured 210Po/210Pb activity disequilibria in the surficial snow of the Arctic Ocean, its age can be constrained. Here, this research compiled the 210Po/210Pb activity ratio of aerosol in the Arctic region as the initial ratio for dating snow. The apparent ages of surficial snow in the Arctic Ocean were estimated based on the measured 210Po/210Pb activity ratio in the surficial snow from the ice stations during the Chinese Ninth Arctic cruise in 2018 and the US GEOTRACES Arctic cruise in 2015. The results showed that the age of snow collected by Chinese ice stations in 2018 ranged from 106 d to 272 d, which was much older than that of snow collected by US ice stations in 2015. The ages of surficial snow showed an obvious latitude effect for both two cruises, indicating that the closer the surficial snow in the Arctic was to the North Pole, the older the snow was. 210Po-210Pb activity disequilibrium can be used as an effective dating tool combined with passive microwave satellite remote sensing technology to constrain the age of ice/snow in the polar region.
Atmospheric deposition is the most important source for 210Po, 210Bi, 210Pb and 7Be radionuclides in the Arctic sea ice regions far away from the influence of rivers and continents. Once the precipitation or snow forms in the Arctic, the falling snow underneath the cloud would be tagged with the specific 210Po/210Pb activity ratio and be locked into a closed environment; as time elapses, this ratio in snow increases to equilibrium state of 210Po-210Pb due to 210Po ingrowth from the decay of 210Pb. From the measured 210Po/210Pb activity disequilibria in the surficial snow of the Arctic Ocean, its age can be constrained. Here, this research compiled the 210Po/210Pb activity ratio of aerosol in the Arctic region as the initial ratio for dating snow. The apparent ages of surficial snow in the Arctic Ocean were estimated based on the measured 210Po/210Pb activity ratio in the surficial snow from the ice stations during the Chinese Ninth Arctic cruise in 2018 and the US GEOTRACES Arctic cruise in 2015. The results showed that the age of snow collected by Chinese ice stations in 2018 ranged from 106 d to 272 d, which was much older than that of snow collected by US ice stations in 2015. The ages of surficial snow showed an obvious latitude effect for both two cruises, indicating that the closer the surficial snow in the Arctic was to the North Pole, the older the snow was. 210Po-210Pb activity disequilibrium can be used as an effective dating tool combined with passive microwave satellite remote sensing technology to constrain the age of ice/snow in the polar region.
2022, 44(9): 124-131.
doi: 10.12284/hyxb2022103
Abstract:
Wave energy attenuation will occur when waves propagating over the permeable seabed, compared with the impermeable seabed. Base on the 1D modified mild slope equation for waves propagating on the permeable seabed, the finite difference model will be set up. The accuracy and applicability of the model will be verified with analytical solution for wave reflection by the rectangular Bragg breakwaters on the impermeable seabed. Furthermore, in case of a permeable seabed, the effects of the sea permeability, the bar width, the bar number and the submergence of the bars on wave reflection coefficient, as well as the difference with the case of an impermeable seabed, will be studied in details. The results show the reflection coefficient of the Bragg resonant reflection increases with the increase in the bar number, and decreases with the increase in the sea permeability and the submergence of the bars. Moreover, there exists a particular value of the bar width that maximizes the Bragg resonant reflection. Compared with the impermeable seabed, the incident wave frequency almost keep the same when Bragg resonance reflection happens, but the reflection coefficient is smaller and zero reflection or full transmission will not exit.
Wave energy attenuation will occur when waves propagating over the permeable seabed, compared with the impermeable seabed. Base on the 1D modified mild slope equation for waves propagating on the permeable seabed, the finite difference model will be set up. The accuracy and applicability of the model will be verified with analytical solution for wave reflection by the rectangular Bragg breakwaters on the impermeable seabed. Furthermore, in case of a permeable seabed, the effects of the sea permeability, the bar width, the bar number and the submergence of the bars on wave reflection coefficient, as well as the difference with the case of an impermeable seabed, will be studied in details. The results show the reflection coefficient of the Bragg resonant reflection increases with the increase in the bar number, and decreases with the increase in the sea permeability and the submergence of the bars. Moreover, there exists a particular value of the bar width that maximizes the Bragg resonant reflection. Compared with the impermeable seabed, the incident wave frequency almost keep the same when Bragg resonance reflection happens, but the reflection coefficient is smaller and zero reflection or full transmission will not exit.
2022, 44(9): 132-144.
doi: 10.12284/hyxb2022089
Abstract:
In the studies of turbulence in coastal and estuary, the turbulence data from field observation is often influenced by noise, which leads to deviate the estimation of turbulence properties. Proper orthogonal decomposition is a method which decompose and reconstruct the flow structure in energy filed. Based on this method, the turbulence data containing noise is denoised combined with numerical experiments and field observation data. The results show that: (1) Proper orthogonal decomposition can remove the noise in turbulence effectively. The percentage of retained energy in reconstruction should be consistent with the percentage of turbulence energy in the raw signal. The results of denoising are related to the percentage of noise, the higher the percentage of noise, the effect of denoising is more obvious. (2) In the field observation, the percentage of noise in the slack tide is obviously higher than the noise which in the non-slack tide, while the percentage of noise in the horizontal direction is higher than that in the vertical direction. The estimation of each turbulence properties is more reasonable after using the proper orthogonal decomposition to denoise.
In the studies of turbulence in coastal and estuary, the turbulence data from field observation is often influenced by noise, which leads to deviate the estimation of turbulence properties. Proper orthogonal decomposition is a method which decompose and reconstruct the flow structure in energy filed. Based on this method, the turbulence data containing noise is denoised combined with numerical experiments and field observation data. The results show that: (1) Proper orthogonal decomposition can remove the noise in turbulence effectively. The percentage of retained energy in reconstruction should be consistent with the percentage of turbulence energy in the raw signal. The results of denoising are related to the percentage of noise, the higher the percentage of noise, the effect of denoising is more obvious. (2) In the field observation, the percentage of noise in the slack tide is obviously higher than the noise which in the non-slack tide, while the percentage of noise in the horizontal direction is higher than that in the vertical direction. The estimation of each turbulence properties is more reasonable after using the proper orthogonal decomposition to denoise.
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