Characteristic disruptions of an excitable carbon cycle
Characteristic disruptions of an excitable carbon cycle
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可兴奋碳循环的特征破坏
DOI：
10.1073/pnas.1905164116
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
D. Rothman
中科院分区：
文献类型：
--
作者：
D. Rothman
地质学过去的巨大环境破坏仍然是个谜。每一次都导致海洋碳储存的暂时变化。尽管原因仍存在争议，但这些变化通常被解释为对外部碳输入的成比例反应。这篇论文提出，许多破坏的程度不是由外部压力的强度决定的，而是由碳循环的内在动力决定的。理论和观测表明，特征性的破坏是由超过阈值的碳流入海洋所激发的。类似的兴奋跟随着强烈而短暂或微弱而持久的流入，只要它们超过阈值。大规模灭绝事件与远高于阈值的流入有关。碳循环的历史被海洋碳储存的神秘的瞬时变化所打断。大规模灭绝总是伴随着这样的破坏，但大多数破坏都相对温和。灾难性较小的群体表现出特有的变化率，而更大的激增则伴随着大规模灭绝。为了更好地理解这些观察，我制定和分析的数学模型，表明中断是由扰动的一个永久稳定的稳态超过阈值。随之而来的激励表现出真实的破坏的特征浪涌。在这种观点中，破坏的幅度和时间尺度是碳循环本身的性质，而不是其扰动。然而，与大规模灭绝相关的激增需要来自外部来源的额外输入，例如大规模火山活动。当二氧化碳以超过阈值的通量进入海洋时，就会激发浪涌。阈值取决于注射的持续时间。在现代碳循环中，对于持续时间为ti = 10，000 y的注入，阈值通量是恒定的;对于较小的ti，阈值的尺度类似于ti−1。因此，现代人为海洋CO2吸收的异常强烈但在地质学上短暂的持续时间，就其激发重大破坏的潜力而言，大致相当于地质学过去与大规模火山活动相关的相对较弱但寿命较长的扰动。
Significance The great environmental disruptions of the geologic past remain enigmatic. Each one results in a temporary change in the oceans’ store of carbon. Although the causes remain controversial, these changes are typically interpreted as a proportionate response to an external input of carbon. This paper suggests instead that the magnitude of many disruptions is determined not by the strength of external stressors but rather by the carbon cycle’s intrinsic dynamics. Theory and observations indicate that characteristic disruptions are excited by carbon fluxes into the oceans that exceed a threshold. Similar excitations follow influxes that are either intense and brief or weak and long-lived, as long as they exceed the threshold. Mass extinction events are associated with influxes well above the threshold. The history of the carbon cycle is punctuated by enigmatic transient changes in the ocean’s store of carbon. Mass extinction is always accompanied by such a disruption, but most disruptions are relatively benign. The less calamitous group exhibits a characteristic rate of change whereas greater surges accompany mass extinctions. To better understand these observations, I formulate and analyze a mathematical model that suggests that disruptions are initiated by perturbation of a permanently stable steady state beyond a threshold. The ensuing excitation exhibits the characteristic surge of real disruptions. In this view, the magnitude and timescale of the disruption are properties of the carbon cycle itself rather than its perturbation. Surges associated with mass extinction, however, require additional inputs from external sources such as massive volcanism. Surges are excited when CO2 enters the oceans at a flux that exceeds a threshold. The threshold depends on the duration of the injection. For injections lasting a time ti≳10,000 y in the modern carbon cycle, the threshold flux is constant; for smaller ti, the threshold scales like ti−1. Consequently the unusually strong but geologically brief duration of modern anthropogenic oceanic CO2 uptake is roughly equivalent, in terms of its potential to excite a major disruption, to relatively weak but longer-lived perturbations associated with massive volcanism in the geologic past.
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