A preliminary study shows that the submarine groundwater discharge（SGD） exists around Taiwan even though groundwater overdrawing on the island is serious. Fifteen of the 20 sites studied for major anions and cations...A preliminary study shows that the submarine groundwater discharge（SGD） exists around Taiwan even though groundwater overdrawing on the island is serious. Fifteen of the 20 sites studied for major anions and cations recorded a clear SGD signal with freshwater outflow. A total of 278 salinity and major ion measurements were made. Sixteen nearly freshwater SGD（salinity≤1.0） samples were obtained, providing strong and direct evidence for the existence of fresh meteoric groundwater entering the ocean from Taiwan. The total SGD flux is estimated to be 1.07×1010 t/a which is about 14% of the annual river output. The freshwater component of the SGD is3.85×109 t which is about 5.2% of the annual river discharge in Taiwan. The collected SGD has a composition similar to seawater with an addition of Ca, CO3 and HCO3 due to dissolution of calcareous rocks. Some samples with high Cl/（Na＋K） may indicate pollution.展开更多
Microtexture analyes on quartz from coastal sediments of the Gulf of Mexico and the Mexican Pacific Coast reveal 35 and 30 types of microtextures,respectively,which were grouped into mechanical,mechanical/chemical and...Microtexture analyes on quartz from coastal sediments of the Gulf of Mexico and the Mexican Pacific Coast reveal 35 and 30 types of microtextures,respectively,which were grouped into mechanical,mechanical/chemical and chemical categories based on their mode of origin.Microtextures of chemical origin are rarer in the El Carrizal than in the Manzanillo beach sediments of the Mexican Pacific Coast.Microtextures of mechanical origin like straight and curved scratches,pits,broken edges,and V-shaped marks indicate high energy,fluvial to marine depositional environments.The scarcity to absence of chemical features suggest that the energy level was higher at the Mexican Pacific coast than on the Gulf of Mexico coast.V-shaped marks are common in the Gulf of Mexico sediments,whereas they are abundant in the quartz grains from the Mexican Pacific coast.Increased frequency and density of V-shaped marks are produced by exceedingly high wave velocity during storm events or tsunamis.Abundance of V-shaped marks with fresh surfaces of quartz grains from the Mexican Pacific coast indicate an extremely high-energy impact event.Many quartz grains from the El Carrizal beach of the Mexican Pacific coast have abundant closely spaced Vshaped marks with fewer fresh surfaces.Such high frequency of V-shaped marks is mainly linked to grain-tograin collision,typically associated with high-energy sub-aqueous conditions with a large volume of sedimentary particles in the water column that are produced during a tsunami or storm events.In contrast,many quartz grains from the Gulf of Mexico have large fresh surfaces with moderate percentages of V-shaped marks that might have been produced by high-energy waves with low sediment concentrations during storm events.展开更多
基金The Aim for the Top University Program of the Ministry of Education under contract No.06C030203the Ministry of Science and Technology of Taiwan under contract No.MOST 105-2611-M-110-017
文摘A preliminary study shows that the submarine groundwater discharge（SGD） exists around Taiwan even though groundwater overdrawing on the island is serious. Fifteen of the 20 sites studied for major anions and cations recorded a clear SGD signal with freshwater outflow. A total of 278 salinity and major ion measurements were made. Sixteen nearly freshwater SGD（salinity≤1.0） samples were obtained, providing strong and direct evidence for the existence of fresh meteoric groundwater entering the ocean from Taiwan. The total SGD flux is estimated to be 1.07×1010 t/a which is about 14% of the annual river output. The freshwater component of the SGD is3.85×109 t which is about 5.2% of the annual river discharge in Taiwan. The collected SGD has a composition similar to seawater with an addition of Ca, CO3 and HCO3 due to dissolution of calcareous rocks. Some samples with high Cl/（Na＋K） may indicate pollution.
基金supported by the Instituto de Geologia,Universidad Nacional Autonoma de Mexico (UNAM),Mexico,through sabbatical project.
文摘Microtexture analyes on quartz from coastal sediments of the Gulf of Mexico and the Mexican Pacific Coast reveal 35 and 30 types of microtextures,respectively,which were grouped into mechanical,mechanical/chemical and chemical categories based on their mode of origin.Microtextures of chemical origin are rarer in the El Carrizal than in the Manzanillo beach sediments of the Mexican Pacific Coast.Microtextures of mechanical origin like straight and curved scratches,pits,broken edges,and V-shaped marks indicate high energy,fluvial to marine depositional environments.The scarcity to absence of chemical features suggest that the energy level was higher at the Mexican Pacific coast than on the Gulf of Mexico coast.V-shaped marks are common in the Gulf of Mexico sediments,whereas they are abundant in the quartz grains from the Mexican Pacific coast.Increased frequency and density of V-shaped marks are produced by exceedingly high wave velocity during storm events or tsunamis.Abundance of V-shaped marks with fresh surfaces of quartz grains from the Mexican Pacific coast indicate an extremely high-energy impact event.Many quartz grains from the El Carrizal beach of the Mexican Pacific coast have abundant closely spaced Vshaped marks with fewer fresh surfaces.Such high frequency of V-shaped marks is mainly linked to grain-tograin collision,typically associated with high-energy sub-aqueous conditions with a large volume of sedimentary particles in the water column that are produced during a tsunami or storm events.In contrast,many quartz grains from the Gulf of Mexico have large fresh surfaces with moderate percentages of V-shaped marks that might have been produced by high-energy waves with low sediment concentrations during storm events.
