Organomineral nanocomposite carbon burial during Oceanic Anoxic Event 2
Organomineral nanocomposite carbon burial during Oceanic Anoxic Event 2
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DOI：
10.5194/bg-11-4971-2014
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发表时间：
2014-09
期刊：
影响因子：
4.9
通讯作者：
S. Löhr;M. Kennedy
中科院分区：
文献类型：
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作者：
S. Löhr;M. Kennedy
海洋缺氧事件（OAE）期间沉积物中有机碳（OC）的富集通常归因于生产力的提高和海洋缺氧。我们发现德梅拉拉海隆塞诺曼阶晚期 OAE 2 的 OC 富集是由缺氧底水、足够的生产力使可用矿物表面饱和以及高表面积碎屑蒙脱石粘土的可变沉积控制的。氧化还原指标显示出一致的缺氧条件，而 OC 浓度与沉积物矿物表面积 (R 2 = 0.92) 之间存在很强的相关性，总有机碳 (TOC) 值范围为 9% 至 33%。 X射线衍射数据表明OC插层在蒙皂石夹层中，而电子、同步加速器红外和X射线显微镜显示粘土矿物和OC之间存在密切联系，这与OC作为有机矿物纳米复合材料和聚集体而不是离散的微米级远洋碎屑的保存相一致。由于 TOC 和矿物表面积之间的一致比率表明相对于表面积的过量 OC 消失了，因此我们认为，在持续缺氧的背景下，蒙脱石供应的变化最能解释有机物富集的变化，这有利于德梅拉拉海隆 OAE 2 期间 TOC 普遍较高。蒙脱石粘土具有独特的能力，能够形成稳定的有机矿物纳米复合材料和聚集体，从而保存有机物，并且是大陆火山沉积物的常见风化产物。蒙脱石通量的增加与高碳埋藏同时发生，与 OAE 2 期间广泛火山活动的证据一致，因此有机矿物碳埋藏可能代表对火山 CO2 脱气的潜在反馈。
Organic carbon (OC) enrichment in sediments de- posited during Oceanic Anoxic Events (OAEs) is commonly attributed to elevated productivity and marine anoxia. We find that OC enrichment in the late Cenomanian aged OAE 2 at the Demerara Rise was controlled by the co-occurrence of anoxic bottom water, sufficient productivity to saturate avail- able mineral surfaces, and variable deposition of high sur- face area detrital smectite clay. Redox indicators show con- sistently oxygen-depleted conditions, while a strong corre- lation between OC concentration and sediment mineral sur- face area (R 2 = 0.92) occurs across a range of total organic carbon (TOC) values from 9 to 33 %. X-ray diffraction data indicate the intercalation of OC in smectite interlayers, while electron, synchrotron infrared and X-ray microscopy show an intimate association between clay minerals and OC, con- sistent with preservation of OC as organomineral nanocom- posites and aggregates rather than discrete, µm-scale pelagic detritus. Since the consistent ratio between TOC and min- eral surface area suggests that excess OC relative to surface area is lost, we propose that it is the varying supply of smec- tite that best explains variable organic enrichment against a backdrop of continuous anoxia, which is conducive to gener- ally high TOC during OAE 2 at the Demerara Rise. Smectitic clays are unique in their ability to form stable organomineral nanocomposites and aggregates that preserve organic matter, and are common weathering products of continental volcanic deposits. An increased flux of smectite coinciding with high carbon burial is consistent with evidence for widespread vol- canism during OAE 2, so that organomineral carbon burial may represent a potential feedback to volcanic degassing of CO2.