全球变化中的浅海沉积作用与物理环境演化——以渤、黄、东海区域为例

SHALLOW MARINE SEDIMENTATION AND PHYSICAL ENVIRONMENT EVOLUTION AS A PART OF GLOBAL CHANGE:AN EXAMPLE FROM THE BOHAI, YELLOW AND EAST CHINA SEA REGIONS

以渤、黄、东海陆架区为例 ,综合评述入海沉积物通量、浅海沉积作用和人类活动影响下的物理环境变化。黄河、长江沉积物入海后主要堆积于河口附近 ,沉积速率为 10～ 10 0mm/a ,部分物质输运至陆架区 ,形成泥质沉积体 ,其沉积速率为 1mm/a量级。但目前河流入海沉积物通量呈减小趋势 ,今后河口附近的堆积将会减缓 ,并在总体上转化为侵蚀状态。在过去的 7ka里 ,来自黄河、长江等河流的沉积物形成了河口三角洲、滨海平原、潮流脊和潮汐汊道沉积体系 ,其演化方式是双重的 ,既有常态边界条件和外力作用下的演化 ,又有边界条件和外力作用发生变异时的演化。边界条件和外力作用变异的原因包括入海通量变化、全球气候变化、海面上升和人类活动等。建议从中国海岸带城市化发展的现状和需求出发 ,对此进行深入研究。

Taking the Bohai, Yellow and East China Sea regions as an example, changes of the physical environment in response to river input, marine sedimentation and anthropogenic activities are reviewed. There is a trend of decrease in water and sediment discharges from the Yellow River; as a result, the Yellow River bed frequently becomes dry. The Yangtze River shows a similar trend; if this trend continues, the cutoffs of water and sediment in the Yangtze River can occur in the 22nd century. In the past, the sediment from the Yellow and Yangtze Rivers accumulated mainly near the river mouth, causing relatively large accretion rates of 10～10 2 mm/a; likewise, a part of the material was transported to seaward, resulting in the formation of shelf mud deposits and an accretion rate of the order of 1 mm/a. However, coastal accretion may be replaced by erosion in response to the decrease in river input. Over the past 7000 years, the accumulation of the river\|derived sediment has formed a variety of sedimentary systems, such as river deltas, coastal plains, tidal ridges and tidal inlets. The evolution of these systems is influenced not only by a constant regime of external forcing, but it is also affected by shift in the external forcing. Such shift results from rapid changes in the river input, global climate, sea level and the intensity of human activities. Further research into changes of the shallow marine physical environment is required for the coastal urbanization and development.