A case study of continental shelf waves in the northwestern South China Sea induced by winter storms in 2021

This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gauge data at stations Hong Kong,Zhapo and Qinglan and sea surface wind data from January 1 to February 28,2021 are used to examine the relationship between along-shelf wind and sea level fluctuation.Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data.The signals are triply peaked at periods of 56 h,94 h and 180 h,propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s.The dispersion relation shows their property of the Kelvin mode of CSW.We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind.The results are comparable with the observation data,suggesting it is effective.The mode 2 CSWs fits very well with the mooring current velocity data.The results from rare current help to understand wave-current interaction in the northwestern SCS.

Measurement of the current and spectral analysis on the continental shelf in the East China Sea

Direct measurements of current velocity and water temperature were undertaken at the mooring Sta. M (125°29.38' N, 31°49.70' E) on the continental shelf area in the East China Sea in June 1999 by R/V Xiangyanghong 14. The relationship between various time series of oceanic fluctuations is calculated by spectral analysis. The major results are as follows: (1) an average (u,v) of (6.9,-3.0 cm/s) at the 30 m depth is obtained during the 9-day observation, and that at the 45 m depth is (3.7,-1.1 cm/s), i. e., the mean flows are southeastward at both the 30 and 45 m depths;the currents become stronger gradually during the observation period; this may be mainly attributed to the transition of the tidal currents from neap to spring; (2)semidiurnal fluctuation is the most dominant in the current fluctuations, and rotates mainly clockwise; in the next place, there is also diurnal fluctuation;the local inertial period is close to the period of diurnal fluctuation, and an inertial motion is clockwise; thus, local inertial motion combines with diurnal fluctuation, and makes the spectral peaks in clockwise components much higher than those in counterclockwise ones; except for the fluctuations of above main periods, there is also the peak at 3 d period for counterclockwise compo-nents in the upper and lower layers; (3) the calculation of cross spectra between two time series of current velocities at the 30 and 45 m depths shows that both the current fluctuations at the 30 and 45 m depths are much alike, i. e., they are synchro; this shows that the flow field here is rather vertically homogeneous; (4)power spectra of tempera-ture time series at both the 30 and 45 m depths show that the semidiurnal peak is the most predominant, and the second highest peak is the diurnal period; besides spectral peaks at above periods, there are also obvious spectral peaks at 6.8 h and 2 d; (5)plots of temperature time series at 16 , 30 , 35 , 45 and 50 m depths show that the temporal variations of temperature at these depths are synchro, which are like those in the velocity field; temperature records also show a gradual rise in temperature, which are also like those in the velocity field.

PROGRESS OF STUDIES ON THE INTERNAL TIDE GENERATED BY THE PASSAGE OF BAROTROPIC TIDE OVER CONTINENTAL SHELF/SLOPE

Various aspects of studies on internal tides are reviewed .Both beam-like structure and modal structure of internal tides may exist in the ocean . Bottom intensifications are caused by many factors .e.g. upstream blocking , which is the result of nonlinear interaction among waves . The energy may decay very fast so that internal tides are mostly locally generated .Internal tides may have considerable residual currents.In a 3-D frame, numerical study revealed that internal waves may interfere with each other to cause strong motions fer from the generation sources.The mechanism that determines how the lee waves break to form various nonlinear waves such as solitary waves, hydraulic jumps and internal surges or bores remains unclear. Analytic study is difficult , so numerical method may be effective . A radiation condition on the open boundary must be employed. A complete 3-D model may gain interesting result.Study on internal tides in China is limited to field observations and data analysis .

Morphological features of continental shelf margin:Examples from the Pakistan Offshore

This paper describes various morphological features of continental shelf and their present-day analogues both present in surface and subsurface data. Most of the examples are taken from Pakistan Offshore.Identification of subsurface features from wireline logs and seismic data is very significant for the application of facies identification in the field of petroleum geosciences, sequence stratigraphy and sedimentology, which is based on the analysis of various lithological characteristic of facies, as well as their geometrical distributions in the basin.

Contribution of Mountain River Materials to the Continental Shelf off Southeastern Hainan Island Since the Mid-Holocene

The concentrations of rare earth elements(REEs)in the bulk sediment of Core X2,which was collected from southeastern Hainan Island,were analyzed to investigate the relative contributions of various provenance regions since mid-Holocene.The results show that sediments in Core X2 were primarily derived from Hainan Island with lesser amounts from Taiwan and limited input from the Pearl River.Based on the application of quantitative inversion to model the REE data,the average contributions of river materials from southeastern Hainan Island and southwestern Taiwan to the study area were 68%and 32%,respectively.Furthermore,starting at 4.0 kyr BP,the transport of fluvial sediments from Taiwan to the study region increased due to enhanced hydrodynamics in South China Sea(SCS).These results indicate that the contributions of mountain river materials from Hainan Island and Taiwan to the continental shelf of northern SCS are non-negligible.Furthermore,these results demonstrate that mountain rivers can play an important role in the material cycle of continental margins and may feature a greater impact than large river systems in specific continental shelf areas.

Provenance of Sediments Filling a Paleo-Channel that Formed on the Western Yellow Sea Continental Shelf During the Last Glacial Period

Several buried paleo-channels are located on the continental shelf of the western Yellow Sea. Research on the paleochannels is significant for both theoretical studies and practical applications. In this paper, we analyse and discuss the mineralogy of sediments in a core(SYS-0803) recovered from a buried paleo-channel on the continental shelf of the western Yellow Sea. The aim is to determine the provenance of sediments that fill the paleo-channel. The heavy mineral assemblage of sediments in the core consists of schistose minerals, common hornblende, epidote, and ilmenite. The light mineral assemblage consists of plagioclase, quartz, lithic fragments, and K-feldspar. Analysis of the compositional maturity of the sand fraction revealed a quartz/feldspar ratio of < 1. A relatively high percentage of smectite is recorded throughout the entire paleo-channel fill, with the greatest percentage in the middle to lower parts. The detrital mineral assemblage and clay mineral content indicate that the paleo-channel sediments were sourced mainly from the Huanghe River during the last glacial period.

pCO_2 distribution and CO_2 flux on the inner continental shelf of the East China Sea during summer 2011

Measurements ofpH, total alkalinity （TA）, partial pressure of CO2 （pCO2） and air-sea CO2 flux （FCO2） were conducted for the inner continental shelf of the East China Sea （ECS） during August 2011. Variations in pCO2 distribution and FCO2 magnitude during the construction of the Three Gorges Dam （TGD） （2003-2009）, and the potential effects of the TGD on the air-sea CO2 exchange were examined. Results showed that the ECS acts as an overall CO2 sink during summer, with pCO2 ranging from 107 to 585 p.atm and an average FCO2 of -6.39 mmol/（m2·d）. Low pCO2 （〈350 μatm） levels were observed at the central shelf （28°-32°N, 123°-125.5°E） where most CO2-absorption occurred. HighpCO2 （〉420 μatm） levels were found in the Changjiang estuary and Hangzhou Bay which acted as the main CO2 source. A negative relationship between pCO2 and salinity （R2=0.722 0） in the estuary zone indicated the predominant effect of the Changjiang Diluted Water （CDW） on the seawater CO2 system, whereas a positive relationship （R2=0.744 8） in the offshore zone revealed the influence of the Taiwan Current Warm Water （TCWW）. Together with the historical data, our results indicated that the CO2 sink has shown a shift southwest while FC02 exhibited dramatic fluctuation during the construction of the TGD, which is located in the middle reaches of the Changjiang. These variations probably reflect fluctuation in the Changjiang runoff, nutrient import, phytoplankton productivity, and sediment input, which are likely to have been caused by the operations of the TGD. Nevertheless, the potential influence of the TGD on the CO2 flux in the ECS is worthy of further study.

Characteristics and evaluation of Mesozoic source rocks in the southeastern East China Sea continental shelf

Source rocks are the material basis of oil and gas generation and determine the potential resources of exploration blocks and have important research value. This paper studies the lithology, thickness, and geochemistry of Mesozoic source rocks in the southeastern East China Sea continental shelf. The results show that the Mesozoic source rocks are mainly dark mudstone and coal-bearing strata. The total thickness of Lower–Middle Jurassic source rocks ranges from 100 m to 700 m, and that of Lower Cretaceous source rocks ranges from 50 m to 350 m. The overall thickness of Mesozoic source rocks is distributed in the NE direction and their thickness center is located in the Jilong Depression. The Lower–Middle Jurassic source rocks are mainly developed shallow marine dark mudstone and transitional coal measure strata. Those of the Lower Cretaceous are mainly mudstone of a fan delta front. Lower –Middle Jurassic and Lower Cretaceous hydrocarbon source rocks are dominated by type III kerogen, with Lower –Middle Jurassic hydrocarbon source rocks having high organic matter abundance and being medium –good hydrocarbon source rocks, while Lower Cretaceous hydrocarbon source rocks have relatively poor quality. From northwest to southeast, the vitrinite reflectance Ro of Mesozoic source rocks increases gradually. Source rocks in the study area are divided into three types. The first hydrocarbon-generating area is mainly located in the southeastern region of the study area, and the Jilong Depression is the hydrocarbongenerating center. The results of this study can provide a basis for exploration of Mesozoic oil and gas resources in the southeastern East China Sea continental shelf.

Observation of continental shelf wave propagating along the eastern Taiwan Strait during Typhoon Meranti 2016

This study is the fi rst to depict typhoon-induced continental shelf wave(CSW)propagation in the eastern Taiwan Strait(TWS)during the passage of Typhoon Meranti in 2016 using tidal gauge data and along-track satellite altimeter data.The strong amplitude response of sea level oscillations(within the range of 0.30–0.54 m)as a free,barotropic CSW after Meranti,which impacted the TWS,was clearly detected in time and frequency(in bands of 64–81 h)using wavelet and cross-wavelet analyses.The measured group and phase speeds were consistent with the dispersion curves for CSW with the fi rst-mode derived from the cross-shelf sections of the eastern TWS,with the mean speeds reaching 3 and 5.6±0.7 m/s,respectively.Coincidentally,the typhoon-induced sea level anomaly(SLA)was also captured by the satellite altimeter before this CSW entered into the TWS.Using the theoretical cross-shore CSW modes to fi t the SLA data,the results indicated that the fi rst three wave modes can interpret this CSW event appeared in the southern TWS very well,with the fi rst mode being the dominant one.

Application of the Three-Dimensional Shallow Sea and Continental Shelf Mode for Inversion of Undercurrent

Abstract. Due to the incapability of high frequency surface wave radar （HFSWR） to detect undercurrent parameters, a new algorithm is proposed to apply a three-dimensional （3D） nonlinear barotropic shallow sea and continental shelf model in coordinate system to the inversion of undercurrent. The calculation domain of this model is the area detected by HFSWR. Considering the benthal topography of the detected area and the ocean dynamic parameters, such as surface current, wind and wave detected by HFSWR, the relation between surface current and undercurrent is established in this model, Accordingly, the undercurrent parameters of corresponding area are obtained. The inversion results agree with the law of ocean dynamics and reproduce the movement of undercurrent.

Vertical Structure of the Tidal Currents on the Continental Shelf of the East China Sea

The available data on tidal currents spanning periods greater than six months for the continental shelf of the East China Sea (26°30.052′N, 122°35.998′E) were analyzed using several methods. Tidal Current Harmonic Analysis results demonstrated that semi-diurnal tides dominated the current movement. The tidal currents of the principal diurnal and semidiurnal rotated clockwise with depth, with the deflection of the major semi-axes to the right in the upper layer and to the left in the lower layer. The vertical structures of two principal semi-diurnal constituents-M2 and S2-were similar, which indicates that the tidal currents are mainly barotropic in this area. The main features of the variation of the four principal tidal constituents with depth demonstrate that the currents in this region are influenced by the upper and lower boundary layers. Therefore, the tidal constituents of the shallow water are similar. Different vertical modes were calculated based on the Empirical Orthogonal Function (EOF) analysis of the Eastern and Northern components of the tidal currents, with a variance contribution for the zero-order model of at least 90%. The variance contribution of the baroclinic model is minimal, which further reveals a strong barotropic character for the tidal currents of this region.

Distribution and influencing factors of acoustic characteristics of seafloor sediment in the Sunda Shelf

To understand the acoustic and physical properties of piston core samples collected from the Sunda continental shelf and analyze their distribution patterns,the samples were analyzed in laboratory,from which three provinces were divided in sound speed,sound speed ratio,porosity,wet bulk density,and maximum shear strength.ProvinceⅠhad lower sound speed and sound speed ratio(<1.04),high porosity,and low wet bulk density.ProvinceⅡhad higher sound speed and sound speed ratio(>1.04),low porosity,and high wet bulk density.ProvinceⅢhad the lowest sound speed and sound speed ratio(0.99),highest porosity(81%),and lowest wet bulk density(1.34 g/cm^(3)).The distribution pattern indicates that sediment movement,sediment source,topography,and hydrodynamic conditions influenced the distribution of acoustic and physical properties.Furthermore,we investigated the relationship of the maximum shear strength to the porosity and wet bulk density,and found that the maximum shear strength was proportional to both the porosity and wet bulk density.This finding has significant implications for ocean engineering applications.

DESERTIZATION OF THE CONTINENTAL SHELF OF CHINA IN THE LATER STAGE OF LATE PLEISTOCENE

In the later stage of Late Pleistocene, global climate entered into the climax period of Wurm when temperature decreased remarkably and glaciers developed. Information from the East China Sea also confirm that the sea level fell by at least 130 m at that time (Emery, 1968). The Bohai Sea and Yellow Sea at the climax period were totally exposed, while the East China Sea and South China Sea shelf regions were exposed partly. The exposed shelf area exceeded 1 million km2 and became a salty desert where land plants could not survive. Such were the conditions which led to the desertization of the shelf region.Eolation was the major exogenetic force not only on land but also on the shelf region in the ice age. At the climax period of Wiirm, the northern part of China developed thick layers of loess deposits. The shelf region at that time had similar climatic conditions and sediments. Because the shelf region was not protected by vegetation in the ice age, intensive wind storms remoulded the primarily

The Weixi High-silica Granitoids in the Central Sanjiang Orogenic Belt,Southwest China:Implications for Growth of the Continental Crust

High-silica granitoids record the formation and evolution of the continental crust.A new intrusive complex has been recognized among silicic volcanic rocks of the Weixi arc,Southwest China.The intrusions consist of granites,granitic porphyries,and granodiorites.Zircon U-Pb age data indicate that the Weixi granitoids formed at 248-240 Ma and were coeval with silicic volcanic rocks of the Weixi arc.The Weixi granitoids are enriched in Rb,Th,and U,depleted in Ba,Sr,Nb,Ta,and Ti,and have high light/heavy rare earth element ratios and slightly negative Eu anomalies.The Weixi granitoids have negative ε_(Nd)(t)values(-9.8 to-7.8)and negative zircon ε_(Hf)(t)values(-12.02 to-5.11).The geochemical and isotopic features suggest the Weixi granitoids were derived by partial melting of ancient crustal material.The Weixi granitoids and silicic volcanic rocks were derived from the same magma by crystal accumulation and melt extraction,respectively,and they record the formation of a continental arc in the central Sanjiang orogenic belt.

Carbon Storage Dynamics in Lower Shimentan Formation of the Qiantang Sag, East China Sea Shelf Basin: Stratigraphy, Reservoir ‒ Cap Analysis, and Source ‒ Sink Compatibility

Excessive carbon emissions have resulted in the greenhouse effect, causing considerable global climate change. Marine carbon storage has emerged as a crucial approach to addressing climate change. The Qiantang Sag(QTS) in the East China Sea Shelf Basin, characterized by its extensive area, thick sedimentary strata, and optimal depth, presents distinct geological advantages for carbon dioxide(CO_(2)) storage. Focusing on the lower section of the Shimentan Formation in the Upper Cretaceous of the QTS, this study integrates seismic interpretation and drilling data with core and thin-section analysis. We reveal the vertical variation characteristics of the strata by providing a detailed stratigraphic description. We use petrophysical data to reveal the development characteristics of high-quality carbon-storage layers and favorable reservoircaprock combinations, thereby evaluating the geological conditions for CO_(2) storage in various stratigraphic sections. We identify Layer B of the lower Shimentan Formation as the most advantageous stratum for marine CO_(2) storage. Furthermore, we analyze the carbon emission trends in the adjacent Yangtze River Delta region. Considering the characteristics of the source and sink areas, we suggest a strong correlation between the carbon emission sources of the Yangtze River Delta and the CO_(2) storage area of the QTS, making the latter a priority area for conducting experiments on marine CO_(2) storage.

Numerical evaluations on the fluid production in the in-situ conversion of continental shale oil reservoirs

In-situ conversion presents a promising technique for exploiting continental oil shale formations,characterized by highly fractured organic-rich rock.A 3D in-situ conversion model,which incorporates a discrete fracture network,is developed using a self-developed thermal-flow-chemical(TFC)simulator.Analysis of the model elucidates the in-situ conversion process in three stages and defines the transformation of fluids into three distinct outcomes according to their end stages.The findings indicate that kerogen decomposition increases fluid pressure,activating fractures and subsequently enhancing permeability.A comprehensive analysis of activated fracture permeability and heating power reveals four distinct production modes,highlighting that increasing heating power correlates with higher cumulative fluid production.Activated fractures,with heightened permeability,facilitate the mobility of heavy oil toward production wells but hinder its cracking,thereby limiting light hydrocarbon production.Additionally,energy efficiency research demonstrates the feasibility of the in-situ conversion in terms of energy utilization,especially when considering the surplus energy from high-fluctuation energy sources such as wind and solar power to provide heating.

Sedimentary systems of the Oligocene Huagang Formation in the central anticline zone of the Xihu Depression,East China Sea Shelf Basin

The Xihu Depression is the largest hydrocarbon-bearing depression of the East China Sea Shelf Basin(also referred to as the ECSSB).However,the depositional systems and reservoir distribution of the Oligocene Huagang Formation in the Xihu Depression are still controversial.Under the guidance of sedimentology and stratigraphy,this study documented a marine-terrestrial transitional environment in the restricted bay setting of the Oligocene Huagang Formation through core description,well logging,and seismic data analysis.This study also revealed that the Oligocene Huagang Formation is dominated by tidal delta,estuary,and gravity flow deposits in the central anticline zone of the Xihu Depression.The new understanding of the sedimentary systems and the discovery of the transgressive gap in the eastern Diaoyu Islands uplift explain the origin of fine-grained sediments and the EW-trending sand bodies in the central depression and the sand bodies parallel to shoreline in the west slope belt,which cannot be explained by previous study results,such as southern transgression or fluvial deltas and even lacustrine deposition.Moreover,the tidal channels,tidal sand flats,and gravity flow sand bodies formed by the transgressive tides are high-quality reservoirs.The study will provide a basis for well placement and serve as guidance for the selection of favorable hydrocarbon exploration areas in the Xihu Depression.

The variation in basal channels and basal melt rates of Pine Island Ice Shelf

In recent years,there has been a significant acceleration in the thinning,calving and retreat of the Pine Island Ice Shelf(PIIS).The basal channels,results of enhanced basal melting,have the potential to significantly impact the stability of the PIIS.In this study,we used a variety of remote sensing data,including Landsat,REMA DEM,ICESat-1 and ICESat-2 satellite altimetry observations,and Ice Bridge airborne measurements,to study the spatiotemporal changes in the basal channels from 2003 to 2020 and basal melt rate from 2010 to 2017 of the PIIS under the Eulerian framework.We found that the basal channels are highly developed in the PIIS,with a total length exceeding 450 km.Most of the basal channels are ocean-sourced or groundingline-sourced basal channels,caused by the rapid melting under the ice shelf or near the groundingline.A raised seabed prevented warm water intrusion into the eastern branch of the PIIS,resulting in a lower basal melt rate in that area.In contrast,a deepsea trough facilitates warm seawater into the mainstream and the western branch of the PIIS,resulting in a higher basal melt rate in the main-stream,and the surface elevation changes above the basal channels of the mainstream and western branch are more significant.The El Ni?o event in 2015–2016 possibly slowed down the basal melting of the PIIS by modulating wind field,surface sea temperature and depth seawater temperature.Ocean and atmospheric changes were driven by El Ni?o,which can further explain and confirm the changes in the basal melting of the PIIS.

A TWO-DIMENSIONAL VORTICITY MODEL OF INTERNAL TIDES GENERATED ON THE CONTINENTAL SHELF/SLOPE

A two-dimensional spectral-difference mode (with vorticity and density equations) of internal tides isdeveloped for studying the genration and propagration of internal tides generated at the continentalshelf/slope. In general, internal tides propagate seaward in deep sea regions and shoreward on the shelf,and are dissipated rapidly. When the Vaisala frequency decreases vertically, waves may be mostly limited to thecontinental slope region. in deep sea region, motions may have either boam-like structure or modal structure,depending on the stratification strerigth and structure, whereas a modal structure may always exist onthe shelf. Waves show strong bottom intensification on the slope when strong stratification exists on thebottom. The barotropic tidal advection may affed the temporal character of internal tides at thecontinental slope, shelf break and shelf regions. but may have little influence on the energy density and energy flux of internal tides. ln the case of strong stratification, waverforms

The continental shelf wave of the East China Sea and its effect on the Kuroshio

The free shelf wave theory is applied to the practical case of the continental shelf in the East China Sea to analyse the effects of the shelf wave on the Kuroshio. The results indicate that the shelf wave in lower frequency travels from north to south and its phase velocity is proportional to the Kuroshio's current velocity) the maximum current velocity of the Kuroshio lies at the continental margin. The analytical solutions obtained indicate that the hydrodynamic characters of the sea region over the shelf present band structure. The horizontal motion ( x -component) caused by the shelf wave at the margin may be one of the causes for generating wavy pattern of the Kuroshio's axis .