The importance of diazotrophic cyanobacteria as primary producers during Cretaceous Oceanic Anoxic Event 2
The importance of diazotrophic cyanobacteria as primary producers during Cretaceous Oceanic Anoxic Event 2
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DOI：
10.5194/bg-3-467-2006
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发表时间：
2006-10
期刊：
影响因子：
4.9
通讯作者：
N. Ohkouchi;Y. Kashiyama;J. Kuroda;N. Ogawa;H. Kitazato
中科院分区：
文献类型：
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作者：
N. Ohkouchi;Y. Kashiyama;J. Kuroda;N. Ogawa;H. Kitazato
**摘要**：在白垩纪大洋缺氧事件2（OAE - 2，约9400万年前）期间沉积的利韦洛·博纳雷利黑色页岩中，块状沉积物的氮同位素组成大多处于–2.7‰至–0.7‰的狭窄范围内。我们还测定了从该黑色页岩中提取的地质卟啉的分子分布和氮同位素组成。C32镍脱氧叶红初卟啉（DPEP）和总镍卟啉的氮同位素组成分别为–3.5‰和–3.3‰，据此我们估计，在博纳雷利黑色页岩形成期间，光合自养细胞的平均氮同位素组成约为 +1‰。这一数值表明固氮作用是这些光合自养生物同化氮的主要过程。此外，主要源自叶绿素a的镍螯合C32 DPEP浓度最高。基于这些证据，我们得出结论，固氮蓝藻是当时的主要初级生产者。在地球历史后半期间歇性出现的黑色页岩型沉积物形成过程中，蓝藻可能是关键的光合自养生物，因此，即使在地球历史的后半期，蓝藻也可能在地球化学循环的演化中发挥了至关重要的作用。
Abstract. In Livello Bonarelli black shale deposited during Cretaceous Oceanic Anoxic Event 2 (OAE-2, ca. 94 Ma), nitrogen isotopic compositions of bulk sediments are mostly in a narrow range from –2.7 to –0.7‰. We also determined molecular distribution and nitrogen isotopic compositions of geoporphyrins extracted from the black shale. The nitrogen isotopic compositions of C32 Ni deoxophylloerythroetioporphyrin (DPEP) and total Ni porphyrins are –3.5 and –3.3‰, respectively, leading us to the estimation that the mean nitrogen isotopic composition of photoautotrophic cells were around +1‰ during the formation of Bonarelli black shale. This value is suggestive of N2-fixation, a dominant process for these photoautotrophs when assimilating nitrogen. Furthermore, Ni-chelated C32 DPEP, derived mainly from chlorophyll a had the highest concentration. Based on this evidence, we conclude that diazotrophic cyanobacteria were major primary producers during that time. Cyanobacteria may be key photoautotrophs during the formation of black shale type sediments intermittently observed throughout the later half of the Earth's history, and hence may have played a crucial role in the evolution of geochemical cycles even in the later half of the Earth's history.