长江口水下三角洲现代沉积速率

长江口水下三角洲采集的两个柱状样放射性核素137Cs分析表明,长江口水下三角洲137Cs剖面中均存在清晰的最大蓄积峰,与1963年的137Cs散落沉降相对应,剖面中同时存在可对应于1959年的较清晰的次级蓄积峰,由此计算得到1959-1964年长江口水下三角洲的平均沉积速率为2.4~4.8 cm/a,1964-2006年减小到1.4~1.8 cm/a。反映出长江口水下三角洲整体淤积速率有很大程度的减小,很可能是三峡蓄水导致流域来沙量大幅度减小所致。虽长江口水下三角洲各处淤积速率减小程度不同,但降低的速度很快,表明长江三角洲发育已出现重大变化,水下三角洲局部地区已观察到侵蚀现象。

MODERN SEDIMENTATION RATE OF THE SUBMARINE DELTA OF THE CHANGJIANG RIVER

Two cores were collected at the submarine delta of the Changjiang River in 2006 and the radionuclide isotope of 137Cs was measured. The 137Cs curves of the two cores clearly show maximum peaks, which correspond to the highest fallout in 1963. Sub-maximum peaks, which may correspond to the fallout in 1959, exist as well in the 137Cs profiles. The depths of the peaks suggest that the average deposition rate of the submarine delta of the Changjiang River ranges from 2.4 cm/a to 4.8 cm/a during 1959-1964, while the average rate changes from 1.4 cm/a to 1.8 cm/a during 1964-2006. It indicates that the deposition rate of the submarine delta decreased, as a rapid response to the dramatic reduction of the sediment discharge after the impoundment of the Three Gorges Reservoir. Even the decrease in the average depositon rate is different from place to place, the decrease is quite high. It suggests that the Changjiang River Delta is suffered from a change, and erosion occurs in some places in the submarine delta already.