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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Ocean methane hydrates as a slow tipping point in the global carbon cycle
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Ocean methane hydrates as a slow tipping point in the global carbon cycle

机译：海洋甲烷水合物是全球碳循环的缓慢转折点

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摘要

We present a model of the global methane inventory as hydrate and bubbles below the sea floor. The model predicts the inventory of CH_4 in the ocean today to be ≈1600-2,000 Pg of C. Most of the hydrate in the model is in the Pacific, in large part because lower oxygen levels enhance the preservation of organic carbon. Because the oxygen concentration today may be different from the long-term average, the sensitivity of the model to O_2 is a source of uncertainty in predicting hydrate inventories. Cold water column temperatures in the high latitudes lead to buildup of hydrates in the Arctic and Antarctic at shallower depths than is possible in low latitudes. A critical bubble volume fraction threshold has been proposed as a critical threshold at which gas migrates all through the sediment column. Our model lacks many factors that lead to heterogeneity in the real hydrate reservoir in the ocean, such as preferential hydrate formation in sandy sediments and subsurface gas migration, and is therefore conservative in its prediction of releasable methane, finding only 35 Pg of C released after 3 ℃ of uniform warming by using a 10% critical bubble volume. If 2.5% bubble volume is taken as critical, then 940 Pg of C might escape in response to 3 ℃ warming. This hydrate model embedded into a global climate model predicts 0.4-0.5 ℃ additional warming from the hydrate response to fossil fuel CO_2 release, initially because of methane, but persisting through the 10-kyr duration of the simulations because of the CO_2 oxidation product of methane.
机译：我们提出了海底以下水合物和气泡形式的全球甲烷存量模型。该模型预测今天海洋中的CH_4存量约为1600-2,000 Pg碳。该模型中的大多数水合物在太平洋中，这在很大程度上是因为较低的氧气含量提高了有机碳的保存能力。因为今天的氧气浓度可能与长期平均值不同，所以该模型对O_2的敏感性是预测水合物清单不确定性的来源。与低纬度地区相比，高纬度地区的冷水柱温度导致北极和南极地区水合物的积累深度更浅。已经提出了临界气泡体积分数阈值作为临界阈值，在该临界阈值处气体全部迁移通过沉积物柱。我们的模型缺乏导致海洋中真正的水合物储层非均质性的许多因素，例如沙质沉积物中优先形成水合物和地下气体迁移，因此对可释放甲烷的预测是保守的，发现仅释放出35 Pg的C通过使用10％的临界气泡体积均匀加热3℃。如果以2.5％的气泡体积为关键，则3℃变暖可能会逸出940 Pg的C。这种嵌入到全球气候模型中的水合物模型预测，水合物对化石燃料CO_2释放的响应将由水合物产生0.4-0.5℃的额外变暖，最初是由于甲烷，但由于甲烷的CO_2氧化产物，模拟过程将持续10个月。

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