Carbon remineralization in the Amazon-Guianas tropical mobile mudbelt: A sedimentary incinerator
Carbon remineralization in the Amazon-Guianas tropical mobile mudbelt: A sedimentary incinerator
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DOI：
10.1016/j.csr.2006.07.016
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发表时间：
2006-11-01
影响因子：
2.3
通讯作者：
Blair, Neal E.
中科院分区：
文献类型：
--
作者：
Aller, Robert C.;Blair, Neal E.
亚马逊河产生了一个巨大的移动的泥带，从赤道到奥里诺科河三角洲延伸了大约1600公里。沉积物沿着亚马逊-圭亚那海岸线的特点是一些最高的C-有机化率报告的河口，三角洲，或货架存款，然而，矛盾的是，除了稳定的红树林或潮间带藻垫，他们通常是suboxic和nonsulfidic。潮汐、风浪和沿岸流的组合形成了大量的流体泥浆和移动的表面沉积层，厚度约为0.5- 2 m，动态回流并经常被再氧化。总的来说，海底的功能就像一个周期性混合的间歇反应器，在一个具有全球重要性的巨大沉积焚化炉中有效地将有机物分解。亚马逊河的材料进入这个动态的分散系统的头部进行初始陆地沉积Corg负载类似于0.7毫克厘米-2颗粒表面积。在近端三角洲顶置中，总的C-org负载降低到类似于0.2 mg Cm-2，类似于其中60-70%仍然是陆地来源。在类似于沿着法属圭亚那600公里下沉流的泥滩中，负荷进一步降低到0.12-0.14毫克厘米-2（60%陆地），与贫营养深海中发现的值相当。法属圭亚那泥滩孔隙沃茨中DOC/Sigma CO2比值表明，> 90%的代谢有机基质被完全氧化。在亚马逊三角洲顶部，在分散系统的头部，陆地和海洋有机质都大大有助于早期成岩成矿作用，虽然反应性海洋基质占主导地位（类似于60-70%）。在三角洲顶集中，陆地C-org的条件速率常数类似于0.2a（-1）。由于沉积碳有机质在运输过程中被耗尽，海洋来源几乎成为唯一的基质，除了非常接近红树林海岸线。泥滩中孔隙水Sigma CO2的C-13和C-14值表明，海岸1 km范围内的矿化有机物的主要来源是少量的炸弹标志性海洋浮游生物（+80 ‰）。因此，新鲜的海洋有机物质不断被夹带到移动的沉积物中，并越来越多地驱动早期成岩反应沿着运输路径。相对难降解的陆地碳-有机质在沉积物中缓慢但稳定地流失。在低海平面期间形成的亚马逊扇沉积物在很大程度上绕过了这种亚氧沉积焚化炉，并以高达现代高海平面内大陆架C-org负荷的3倍的相似量储存物质（Keil等人，1997年b。海洋钻探计划会议录，科学成果。第155卷pp. 531-537）。沉积动力学，包括频率和规模的再活化，和分散系统的性质显然是关键的控制成岩过程，地球化学循环，以及全球碳存储沿着大陆边缘。(c)2006爱思唯尔有限公司保留所有权利。
The Amazon River spawns a vast mobile mudbelt extending similar to 1600 km from the equator to the Orinoco delta. Deposits along the Amazon-Guianas coastline are characterized by some of the highest C-org remineralization rates reported for estuarine, deltaic, or shelf deposits, however, paradoxically, except where stabilized by mangroves or intertidal algal mats, they are usually suboxic and nonsulfidic. A combination of tides, wind-driven waves, and coastal currents forms massive fluid muds and mobile surface sediment layers similar to 0.5-2m, thick which are dynamically refluxed and frequently reoxidized. Overall, the seabed functions as a periodically mixed batch reactor, efficiently remineralizing organic matter in a gigantic sedimentary incinerator of global importance. Amazon River material entering the head of this dynamic dispersal system carries an initial terrestrial sedimentary Corg loading of similar to 0.7 mg Cm-2 particle surface area. Total C-org loading is lowered to similar to 0.2 mg Cm-2 in the proximal delta topset, similar to 60-70% of which remains of terrestrial origin. Loading decreases further to 0.12-0.14 mg Cm-2 (similar to 60% terrestrial) in mudbanks similar to 600 km downdrift along French Guiana, values comparable to those found in the oligotrophic deepsea. DOC/Sigma CO2 ratios in pore waters of French Guiana mudbanks indicate that > 90% of metabolized organic substrates are completely oxidized. Within the Amazon delta topset at the head of the dispersal system, both terrestrial and marine organic matter contribute substantially to early diagenetic remineralization, although reactive marine substrate dominates (similar to 60-70%). The conditional rate constant for terrestrial C-org in the delta topset is similar to 0.2 a(-1). As sedimentary C-org is depleted during transit, marine sources become virtually the exclusive substrate for remineralization except very near the mangrove shoreline. The delta C-13 and Delta C-14 values of pore water Sigma CO2 in mudbanks demonstrate that the primary source of remineralized organic matter within similar to 1 km of shore is a small quantity of bomb signature marine plankton (+ 80 parts per thousand). Thus, fresh marine organic material is constantly entrained into mobile deposits and increasingly drives early diagenetic reactions along the transit path. Relatively refractory terrestrial C-org is lost more slowly but steadily during sedimentary refluxing and suboxic diagenesis. Amazon Fan deposits formed during low sea level stand largely bypassed this suboxic sedimentary incinerator and stored material with up to similar to 3X the modern high stand inner shelf C-org load (Keil et al., 1997b. Proceedings of the Ocean Drilling Program, Scientific Results. Vol. 155. pp. 531-537). Sedimentary dynamics, including frequency and magnitude of remobilization, and the nature of dispersal systems are clearly key controls on diagenetic processes, biogeochemical cycling, and global C storage along the continental margins. (c) 2006 Elsevier Ltd. All rights reserved.