Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea
Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea
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DOI：
10.1029/2010pa001993
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发表时间：
2011-05-11
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影响因子：
--
通讯作者：
Hinrichs, Kai-Uwe
中科院分区：
文献类型：
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作者：
Cook, Mea S.;Keigwin, Lloyd D.;Hinrichs, Kai-Uwe
关于海洋甲烷水合物在末次冰河期大气甲烷浓度和气候变化中的作用存在争议。在这项对白令海东南部（700 m 和 1467 m 水深）的两个沉积物岩心的研究中，我们确定了末次冰期期间到达海底的强烈甲烷通量的多个事件。在放射性碳年龄模型的不确定性范围内，这些事件在两个核心中是同时发生的，并且与 Dansgaard-Oeschger 事件具有相似的时间和持续时间。这些事件的标志是沉积层中含有 C-13 贫乏的自生碳酸盐矿物； C-13 耗尽的古细菌和细菌脂质，类似于 ANME-1 型厌氧甲烷氧化微生物群落中发现的脂质；底栖有孔虫丰度和物种分布的变化。两个岩心中自生碳酸盐的相似时间和同位素组成与区域范围内含甲烷流体向上通量的增加一致。这项研究是圣巴巴拉盆地以外首次对冰川沉积物中普遍、重复的甲烷通量进行观测。然而，与“笼形枪假说”（Kennett et al., 2003）相反，这些取心位置太深，不足以成为甲烷水合物不稳定的原因，这意味着海洋沉积甲烷的大部分可能参与千年时间尺度的气候或碳循环反馈。我们推测，这些富含蛋白石的沉积物中的甲烷脉冲可能是由于二氧化硅成岩作用逐渐积累的孔隙流体中超压的突然释放引起的。此次释放可能是由阿留申俯冲带的地震震动引发的，该地震震动是由于间质层开始时海平面上升引起的静水压力增加而引起的。
There is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period. In this study of two sediment cores from the southeast Bering Sea (700 m and 1467 m water depth), we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor. Within the uncertainty of the radiocarbon age model, the episodes are contemporaneous in the two cores and have similar timing and duration as Dansgaard-Oeschger events. The episodes are marked by horizons of sediment containing C-13-depleted authigenic carbonate minerals; C-13-depleted archaeal and bacterial lipids, which resemble those found in ANME-1 type anaerobic methane oxidizing microbial consortia; and changes in the abundance and species distribution of benthic foraminifera. The similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region-wide increase in the upward flux of methane bearing fluids. This study is the first observation outside Santa Barbara Basin of pervasive, repeated methane flux in glacial sediments. However, contrary to the "Clathrate Gun Hypothesis" (Kennett et al., 2003), these coring sites are too deep for methane hydrate destabilization to be the cause, implying that a much larger part of the ocean's sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales. We speculate that pulses of methane in these opal-rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis. The release could be triggered by seismic shaking on the Aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials.