CO2 Release From Pockmarks on the Chatham Rise‐Bounty Trough at the Glacial Termination
CO2 Release From Pockmarks on the Chatham Rise‐Bounty Trough at the Glacial Termination
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DOI：
10.1029/2019pa003674
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发表时间：
2019-11
影响因子：
3.5
通讯作者：
L. Stott;B. Davy;Jun Shao;R. Coffin;I. Pecher;H. Neil;P. Rose;J. Bialas
中科院分区：
文献类型：
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作者：
L. Stott;B. Davy;Jun Shao;R. Coffin;I. Pecher;H. Neil;P. Rose;J. Bialas
新西兰查塔姆隆起、坎特伯雷陆架和内邦蒂海槽上5万平方公里的面积上出现了大小不一的海底麻点。麻点集中在平坦俯冲的Hikurangi高原上方。回声探测仪的数据确定麻点形成的重复事件发生在大约10万年的频率上，与更新世冰川终止重合。在这里，我们展示了在较大的凹坑下面有结构性的管道，流体通过这些管道向上流向海底。在最后一次冰川终止时，这些海底管道旁边的海洋沉积物和麻点中记录了大量负的Δ14C漂移。现代孔隙水不含甲烷，在冰川端部不存在负的δ13C漂移，这将指示Δ14C漂移和麻点产生时的甲烷或地幔碳。配备了同位素示踪剂的海洋环流模型无法模拟查塔姆海隆上通过输送东太平洋海隆释放的热液碳而产生的这些大规模的Δ14C漂移，这是先前的研究表明的。在这里，我们将Δ的14C异常和麻点归因于从地下储集层释放14C死亡的二氧化碳和富碳流体，最有可能的是晚白垩世俯冲到隆起以下的中生代碳酸盐。由于Δ14C异常的大量麻点和持续时间，麻点可能共同代表着14C的一个重要来源-冰川终止期间海洋的死碳。
Seafloor pockmarks of varying size occur over an area of 50,000 km2 on the Chatham Rise, Canterbury Shelf and Inner Bounty Trough, New Zealand. The pockmarks are concentrated above the flat‐subducted Hikurangi Plateau. Echosounder data identify recurrent episodes of pockmark formation at ~100,000‐year frequency coinciding with Pleistocene glacial terminations. Here we show that there are structural conduits beneath the larger pockmarks through which fluids flowed upward toward the seafloor. Large negative Δ14C excursions are documented in marine sediments deposited next to these subseafloor conduits and pockmarks at the last glacial termination. Modern pore waters contain no methane, and there is no negative δ13C excursion at the glacial termination that would be indicative of methane or mantle‐derived carbon at the time the Δ14C excursion and pockmarks were produced. An ocean general circulation model equipped with isotope tracers is unable to simulate these large Δ14C excursions on the Chatham Rise by transport of hydrothermal carbon released from the East Pacific Rise as previous studies suggested. Here we attribute the Δ14C anomalies and pockmarks to release of 14C‐dead CO2 and carbon‐rich fluids from subsurface reservoirs, the most likely being dissociated Mesozoic carbonates that subducted beneath the Rise during the Late Cretaceous. Because of the large number of pockmarks and duration of the Δ14C anomaly, the pockmarks may collectively represent an important source of 14C‐dead carbon to the ocean during glacial terminations.