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Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea

机译：白令海东南部冰川沉积物中记录的垂直甲烷通量重复脉冲

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摘要

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 ~(13)C-depleted authigenic carbonate minerals; ~(13)C-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.
机译：在上一个冰川期，海洋甲烷水合物在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（水深700 m和1467 m）的两个沉积物岩心的研究中，我们确定了在最后一次冰川期强烈的甲烷通量到达海底的冰期。在放射性碳年龄模型的不确定性范围内，这两个事件的发作时间是同时发生的，并且与Dansgaard-Oeschger事件的发生时间和持续时间相似。这些事件以含〜（13）C的自生碳酸盐矿物的沉积物层位为标志。 〜（13）C耗尽的古细菌和细菌脂质，类似于在ANME-1型厌氧甲烷氧化微生物菌群中发现的脂质;底栖有孔虫的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含甲烷流体的向上通量在整个区域的增加一致。这项研究是圣塔芭芭拉盆地以外首次对冰川沉积物中普遍存在的甲烷通量进行观测的结果。但是，与“包合物枪假说”（Kennett等人，2003）相反，这些取芯点太深，无法引起甲烷水合物的失稳，这意味着海洋中很大一部分沉积甲烷可能参与了气候变化或千年周期的碳循环反馈。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孔隙流体中的超压突然释放引起的，而超压随着二氧化硅的成岩作用而逐渐积累。释放可能是由阿留申俯冲带上的地震震动引起的，该震动是由陆际开始时与海平面上升有关的静水压力增加引起的。

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