南海中沙群岛以北至陆坡表层沉积物碳酸钙含量的分布

Distribution of Carbonate Content in Surface Sediment from North of Zhongsha Islands to Northern Slope in the South China Sea

对南海北部(16°―20°N、114°―116°E)区域、285～4 175 m水深范围内78个表层样进行了碳酸钙含量分析。表层样碳酸钙含量变化范围是1.3%～87.8%,平均约25.6%;碳酸钙含量具有随水深增大而减小的趋势,在北部陆坡和中沙北海岭,碳酸钙含量突然变小的界面分别位于水深约3 000 m、3 250 m处。中沙北海岭碳酸钙含量40%等值线水深变化介于2 500～3 900 m之间,北部陆坡碳酸钙含量20%等值线水深范围约为2 180～3 515 m;碳酸钙含量10%等值线水深变化相对较小,在16°～17.5°N和17.5°～20°N范围内平均水深分别约4 009 m、3 551 m。研究区碳酸钙溶跃面可能位于水深约3 000 m处。18°N以北区域比18°N以南区域的陆源物质稀释作用强,且二者间陆源物质稀释作用强度的差异随水深从2 000 m增至3 000 m而逐渐减小,在水深超过3 000 m后基本保持不变。

Carbonate content analysis is carried out for 78 surface sediment samples taken from the northern part of the South China Sea（114°-116°E,16°-20°N;samples cover the depth range of 285-4175 m）.The surface sediment carbonate contents change from 1.3% to 87.8%,the average content is 25.6%,and the carbonate content decreases with the increase of water depth,which shows an abrupt decrease at water depth about 3000 m on the northern slope and about 3250 m on the Zhongshabei ridge,respectively.The isoline of carbonate content 40% has a water depth range of 2500-3900 m on the Zhongshabei ridge,the isoline of carbonate content 20% has a water depth range of 2180-3515 m on the northern slope,while the isoline of carbonate content 10% has a relative small water depth range with the average water depth of 4009 m in 16-17.5°N and of 3551 m in 17.5-20°N.The lysocline in the study area is likely located at water depth of about 3000 m.The region north of 18°N has a stronger terrigenous material dilution than the region south of 18°N,while the difference of terrigenous material dilution in the two regions becomes smaller with the increase of water depth from 2000-3000 m and nearly keeps stable beyond the water depth 3000 m.