Distribution and sources of organic carbon, nitrogen and their isotopic signatures in sediments from the Ayeyarwady (Irrawaddy) continental shelf, northern Andaman Sea
Distribution and sources of organic carbon, nitrogen and their isotopic signatures in sediments from the Ayeyarwady (Irrawaddy) continental shelf, northern Andaman Sea
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DOI：
10.1016/j.marchem.2008.04.006
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发表时间：
2008-09
期刊：
影响因子：
3
通讯作者：
V. Ramaswamy;B. Gaye;P. Shirodkar;P. S. Rao;A. Chivas;D. J. Wheeler;Swe Thwin
中科院分区：
文献类型：
--
作者：
V. Ramaswamy;B. Gaye;P. Shirodkar;P. S. Rao;A. Chivas;D. J. Wheeler;Swe Thwin
通过对北方安达曼海伊洛瓦迪陆架110个沉积物样品的TOC、TN及其δ 13 C、δ 15 N值的测定，探讨了沉积物中有机质的含量和来源。相对较高的TOC和TN浓度被发现在内陆架泥带，并在大陆坡沉积物，而外架沉积物，主要由残留砂，是低的TOC。TOC含量与细粒沉积物丰度呈正相关。TOC：TN比值和δ 13 C和δ 15 N值在现代内陆架泥带和Martaban湾内显示低变异性，表明相似的来源。内陆架泥带的TOC：TN比值大多在6 ~ 8之间，这些值与伊洛瓦迪河和萨尔温江的悬浮沉积物相似。有机物的δ 13 C值从Martaban湾的−25‰增加到斜坡地区的约−22‰，表明远离海岸的陆地输入减少。伊洛瓦迪陆架的δ 15 N值较低（+3.3 ~+4.8‰），尤其是在伊洛瓦迪河口附近，反映了淡水和陆源输沙的影响较大。一个简单的两个端元碳混合模型适用于伊洛瓦迪陆架区表明，陆源贡献了超过70%的有机碳在现代泥带的内陆架和海湾的Martaban。陆源有机碳的百分比逐渐减少近海，减少到低于60%的大陆架边缘附近。一个强大的陆源信号被保存在内陆架和海湾的Martaban沉积物可能是因为有机质从源区是不受密集的加工和替换在洪泛平原和三角洲地区，以及快速埋葬在海上。
Total organic carbon (TOC), total nitrogen (TN) and their δ13C and δ15N values were determined from 110 sediment samples from the Ayeyarwady (Irrawaddy) continental shelf, northern Andaman Sea to decipher the concentration and source of organic matter. Comparatively higher TOC and TN concentrations are found in the inner-shelf mud belt, and on the continental slope sediments, whereas the outer-shelf sediments, composed mostly of relict sands, are low in TOC. The TOC contents are positively correlated with the abundance of fine-grained sediments. The TOC:TN ratios and δ13C and δ15N values show low variability within the modern inner-shelf mud belt and Gulf of Martaban, indicating similar source. The TOC:TN ratios are mostly between 6 and 8 in the inner-shelf mud belt and these values are similar to the suspended sediments in the Ayeyarwady and Salween rivers. The δ13C values of organic matter increase from −25‰ in the Gulf of Martaban to about −22‰ in the slope regions indicating decreasing terrestrial input away from the coast. The δ15N values on the Ayeyarwady shelf are rather low (+3.3 to +4.8‰), especially off the mouths of the Ayeyarwady River mouths, reflecting greater influence of freshwater and terrigenous sediment discharge. A simple two end-member carbon mixing model applied to the Ayeyarwady shelf region indicates that terrigenous sources contribute more than 70% of the organic carbon in the modern mud belt in the inner shelf and Gulf of Martaban. Terrigenous organic carbon percentages reduce gradually offshore, reducing to less than 60% near the continental shelf edge. A strong terrigenous signal is preserved in the inner shelf and Gulf of Martaban sediments probably because organic matter from the source region is not subject to intensive processing and replacement in the floodplains and deltaic regions as well as rapid burial at sea.