Evolution of carbon cycle over the past 100 million years
Evolution of carbon cycle over the past 100 million years
复制标题
DOI：
10.1016/j.gca.2012.10.014
复制
发表时间：
2013-02
影响因子：
5
通讯作者：
Gaojun Li;H. Elderfield
中科院分区：
文献类型：
--
作者：
Gaojun Li;H. Elderfield
一般认为，晚白垩世以来全球气候的逐渐变冷是大气CO2分压（pCO2）降低的结果。然而，关于碳循环如何以及为什么演变以及它如何影响pCO2的细节尚未完全解决。虽然pCO2的长期下降可能是由于火山脱气通过pCO2和硅酸盐风化之间的负反馈减少，海底扩张，CO2脱气的主要控制，似乎一直保持相对稳定。另一种解释，称为“隆起驱动气候变化”假说，提出构造隆起可能通过硅酸盐风化增强了大气CO2的汇，从而导致pCO2的下降。然而，增加风化汇的CO2可以耗尽大气中所有的CO2在几百万年内，而保持火山出气恒定。本文基于海洋碳、锶、锇同位素记录和海底扩张速率约束的反演模型，计算了长期碳循环的主要通量。在新的模式中，岛玄武岩和大陆硅酸盐岩的风化作用被分开。结果表明，岛屿玄武岩风化的长期下降与过去1亿年来全球变冷的趋势一致。碳酸盐岩风化作用、逆风化作用、火山岩脱气作用以及有机碳储层的发育都伴随着CO2通量的剧烈变化。这些通量对大气CO2循环的干扰似乎是通过对温度和径流等pCO2控制的环境因素敏感的岛屿玄武岩风化的伴随调整来维持的。pCO2与岛屿玄武岩风化之间的负反馈作用可能对长期碳循环的稳定起着重要作用。
It is generally accepted that progressive cooling of global climate since the Late Cretaceous results from decreasing partial pressure of atmospheric CO2(pCO2). However, details on how and why the carbon cycle evolved and how it would affect pCO2have not been fully resolved. While the long-term decline of pCO2might be caused by the decrease of volcanic degassing through the negative feedback between pCO2and silicate weathering, seafloor spreading, the major control of CO2degassing, seems to have remained relatively constant. Alternative explanation, known as ‘uplift driven climate change’ hypothesis, proposes that tectonic uplift may have enhanced the sink of atmospheric CO2by silicate weathering, and thus produced the decline of pCO2. However, increasing weathering sink of CO2could deplete atmosphere all of its CO2within several million years while holding volcanic outgassing constant. In this work, major fluxes of long-term carbon cycle are calculated based on a reverse model constrained by marine C, Sr and Os isotopic records and the spreading rate of sea floor. Weathering of island basalt and continental silicate rocks are separated in the new model. The results indicate a long-term decline of island basalt weathering in consistent with the global cooling trend over the past 100 million years. Dramatic changes of the CO2fluxes associated continental silicate weathering, reverse weathering, volcanic degassing and the growth of organic carbon reservoir have been observed. Disturbance of atmospheric CO2cycle by these fluxes seems to be maintained by the concomitant adjustments of island basalt weathering that were sensitive to the pCO2controlled environment factors such as temperature and runoff. The negative feedbacks between pCO2and weathering of island basalt might have played a significant role in stabilizing the long-term carbon cycle.