A DTM map of the study area in the Taiwan Shoal was drawn based on precise and high- density data acquired in a field survey by a multi-beam sounding system （R2Sonic2024）. We identified sand waves in the study area ...A DTM map of the study area in the Taiwan Shoal was drawn based on precise and high- density data acquired in a field survey by a multi-beam sounding system （R2Sonic2024）. We identified sand waves in the study area at water depths of 13.89-49.12 m; the main sand waves had heights of 5- 25 m, lengths of 0.1-2.0 km, and crest lines 0.1-6.5 km long. The spatial distribution of the sand waves on the seabed is dense in the north and sparse in the south and the directions range between 50°-80° and 90°-135°. Between the main sand waves, secondary sand waves develop with heights of 0.1-5.0 m and lengths of 10-100 m, which are difficult to detect by satellite remote sensing. By comparing the evolution structures of the secondary and main sand waves, we identified three evolution modes of the secondary sand waves： parallel, oblique, and divergent modes according to the relative crest directions. Suitable water depth, reciprocating current speeds between 40 and 100 cm/s, and abundant sediment supply create favorable conditions for the formation of linear sand waves. Comparing the DTM maps and profiles of the June 2012 and June 2013 surveys of the same area, we found that the shape and morphology of the sand waves remained mostly unchanged under normal hydrodynamic conditions.展开更多
Based on the latest submarine topography data of the China 908 Project （China offshore marine environmental comprehensive investigation and assessment）,we analyzed the general China offshore submarine topographical ...Based on the latest submarine topography data of the China 908 Project （China offshore marine environmental comprehensive investigation and assessment）,we analyzed the general China offshore submarine topographical characteristics and the factors influencing its development.The submarine topography off the coast of China follows the NW-SE trend of the land topography.The gradient of the submarine topography ranges from 0.2％ to 1.6％ with an average gradient of about 0.8％.The depth contours run mostly parallel to the coast,and extend out to sea in estuary areas.The submarine topography is dominated by the geological structure,which shows the typical characteristics of two uplifts and two subsidence events from north to south.The geological structure combined with the different sedimentary environments and complex hydrodynamic conditions produced topography that can be characterized by three types：sedimentary basins,compressionuplift,and transition form.In the sedimentary basin and compression-uplift regions,the topographical undulation is small,sediments are fine-grained,and the currents flow in a single direction,leading to bays with sedimentary plains and underwater accumulation slopes,which are of the same tectonic origin.Transition-type topography is characterized by strong undulations and mixed-size sediment particles,terraces and scarps inshore and shelf plains and erosion-deposition landforms offshore.This is a result of incomplete fault block development and repeated transgressions.In the deposition reformation regions （transition form type）,the topography has strong undulations,the sediments are coarse,tidal sand ridges are well-developed at terrigenoussupplied estuaries and convergence zones,and the Holocene sediments are thick,transformed by tides,river runoff,and currents.展开更多
基金Funding was provided by the Marine Public Special Project (201105001 and 201205004)the Natural Science Foundation (China project, 41276058)
文摘A DTM map of the study area in the Taiwan Shoal was drawn based on precise and high- density data acquired in a field survey by a multi-beam sounding system （R2Sonic2024）. We identified sand waves in the study area at water depths of 13.89-49.12 m; the main sand waves had heights of 5- 25 m, lengths of 0.1-2.0 km, and crest lines 0.1-6.5 km long. The spatial distribution of the sand waves on the seabed is dense in the north and sparse in the south and the directions range between 50°-80° and 90°-135°. Between the main sand waves, secondary sand waves develop with heights of 0.1-5.0 m and lengths of 10-100 m, which are difficult to detect by satellite remote sensing. By comparing the evolution structures of the secondary and main sand waves, we identified three evolution modes of the secondary sand waves： parallel, oblique, and divergent modes according to the relative crest directions. Suitable water depth, reciprocating current speeds between 40 and 100 cm/s, and abundant sediment supply create favorable conditions for the formation of linear sand waves. Comparing the DTM maps and profiles of the June 2012 and June 2013 surveys of the same area, we found that the shape and morphology of the sand waves remained mostly unchanged under normal hydrodynamic conditions.
基金granted by the National Science Foundation of China (No. 41276058)the project of integrated achievement on investigation of submarine topography and geomorphology in offshore China (No. 908-ZC-I-07)the State Oceanic Administration public welfare research project (No. 201105001, No. 2012418004)
文摘Based on the latest submarine topography data of the China 908 Project （China offshore marine environmental comprehensive investigation and assessment）,we analyzed the general China offshore submarine topographical characteristics and the factors influencing its development.The submarine topography off the coast of China follows the NW-SE trend of the land topography.The gradient of the submarine topography ranges from 0.2％ to 1.6％ with an average gradient of about 0.8％.The depth contours run mostly parallel to the coast,and extend out to sea in estuary areas.The submarine topography is dominated by the geological structure,which shows the typical characteristics of two uplifts and two subsidence events from north to south.The geological structure combined with the different sedimentary environments and complex hydrodynamic conditions produced topography that can be characterized by three types：sedimentary basins,compressionuplift,and transition form.In the sedimentary basin and compression-uplift regions,the topographical undulation is small,sediments are fine-grained,and the currents flow in a single direction,leading to bays with sedimentary plains and underwater accumulation slopes,which are of the same tectonic origin.Transition-type topography is characterized by strong undulations and mixed-size sediment particles,terraces and scarps inshore and shelf plains and erosion-deposition landforms offshore.This is a result of incomplete fault block development and repeated transgressions.In the deposition reformation regions （transition form type）,the topography has strong undulations,the sediments are coarse,tidal sand ridges are well-developed at terrigenoussupplied estuaries and convergence zones,and the Holocene sediments are thick,transformed by tides,river runoff,and currents.
