孟加拉湾中部表层沉积物有机碳分布特征及来源

Distribution and Source of Organic Carbon in Surface Sediment From Mid-Bengal Bay

通过对孟加拉湾中部110个表层沉积物样品有机碳、氮含量及粒度进行测试分析,揭示了研究区表层沉积物平均粒径、有机碳(TOC)、总氮(TN)、有机碳/总氮(TOC/TN)的分布特征,并讨论了其有机质来源及控制因素。结果表明,研究区表层沉积物的平均粒径值为6.2~7.6Φ,平均为7.1Φ,其分布呈现出以16°N和15°N为界南北两侧海域粒度相对较细(>7Φ),中间海域相对较粗(<7Φ)的特点;研究区TOC的质量分数为0.37%~1.24%,平均为0.84%,TN质量分数为0.05%~0.15%,平均为0.10%,两者分布特点相似,大致以15°N和16°N为界表现出南北两侧海域高,中间海域低的特点;TOC/TN比值为6.05~12.88,平均为8.38,中部海域比值高,南北两侧低。根据TOC/TN比值估算研究区陆源和海洋自生有机质的贡献,结果表明研究区陆源与海洋自生有机质平均相对贡献分别为60%和40%。研究区有机质的分布主要受控于有机质来源及输运方式,其中浊流输运导致的溢流沉积是其最主要的控制因素。另外,粒度、河流悬浮体的输入沉降和有机质保存条件等因素也起着重要作用。

This study analyzed total organic carbon （TOC） ,total nitrogen （TN） and grain size of 110 surface samples from the mid-Bengal Bay,indicated their distributional patterns of some proxies such as mean grain size （Mz） ,TOC,TN and TOC/TN,and then discussed the origin of organic matter and its controlling factors.The Mz varies in a range of 6.2-7.6 Ф,with an average of 7.1 Ф.The distribution features of Mz, TOC,TN and TOC/TN are generally similar,and all of them show the same two ＂boundaries＂： 15°N and 16°N, And, based on these two boundaries, the study area can be subdivided into the following three parts, northern,central and southern area.For Mz,it is fine-grained in the northern and southern areas （〉7 Ф） and coarse in the central area （〈7 Ф）.Contents of TOC and TN vary in a range of 0.37%-1.24% with an average of 0.84% and 0.05%-0.15% with an average of 0.10% ,respectively.Compared to those in the cen- tral area,the contents of both TOC and TN in the northern and southern areas are higher.TOC/TN varies in a range of 6.05-12.88 with an average of 8.38 ,which are higher in the central area than the northern and southern areas.According to the TOC/TN ratios, we estimated the average contributions of terrigenous and oceanic organic matter to the study area, 60% and 40%, respectively. We suggested that the distribution pattern of organic matter in the study area are mainly controlled by material sources and supply paths,and the most important factor is the overflowing sediments caused by turbidity currents.In addition,some other factors such as grain size, sedimentation of suspended materials （carried by the river plume） and preserva tion conditions for organic matters,play important role as well.