地学前缘 ›› 2023, Vol. 30 ›› Issue (3): 313-339.DOI: 10.13745/j.esf.sf.2022.12.51

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碳的固定、运输、转移和排放过程:对地球深部碳循环的启示

陈雪倩(), 张立飞*()   

  1. 北京大学 地球与空间科学学院, 北京 100871
  • 收稿日期:2022-09-14 修回日期:2022-12-15 出版日期:2023-05-25 发布日期:2023-04-27
  • 通讯作者: *张立飞(1963—),男,博士生导师,主要从事变质地质学研究工作。E-mail: lfzhang@pku.edu.cn
  • 作者简介:陈雪倩(1996—),女,博士研究生,矿物学、岩石学、矿床学专业。E-mail: chenxueqian@pku.edu.cn
  • 基金资助:
    国家重点研发计划项目(2019YFA0708501)

Carbon sequestration, transport, transfer, and degassing: Insights into the deep carbon cycle

CHEN Xueqian(), ZHANG Lifei*()   

  1. School of Earth and Space Sciences, Peking University, Beijing 100871, China
  • Received:2022-09-14 Revised:2022-12-15 Online:2023-05-25 Published:2023-04-27

摘要:

俯冲带背景下,碳在促进岩石熔融、岩浆起源和演化、地球深部的岩石学及动力学等过程中扮演的角色尤为重要。碳的存在形式是由温度、压力、氧逸度以及溶流体的性质等条件控制的,这些以不同形式存在的碳随板块俯冲到达地球深部,而后又通过火山作用等脱气过程被返回地表,便形成了地球深部碳循环过程。固碳和脱碳反应是影响碳在固体地球、海洋和大气圈转换的主要反应。碳的固定包括硅酸盐风化作用、玄武质洋壳的热液交代、海沟外隆的蛇纹石化、有机碳的埋藏和逆风化作用等过程;碳的运输包括沉积成因和交代成因沉积物的俯冲过程;当俯冲碳被输送到地球内部时,它可能被保留在板块内,或者转移到地幔楔中,又或再被循环到地球深部,这将取决于特定构造环境的温压条件和氧化还原状态等。碳的排放包括火山作用、弧前扩散脱气、溶解脱碳、变质反应脱碳和熔融脱碳等过程,这些过程将俯冲下去的碳再一次返回大气,能够平衡俯冲带的碳输入。本文系统地总结了地表及地球深部碳的固定、运输、转移和排放过程中碳的存在形式、碳的迁移和变化以及相关碳通量计算值,分析了目前碳通量差异的原因并阐述了今后需要深入研究的一些关键科学问题。另外,工业革命后,人为成因的CO2释放对于全球气候产生了巨大影响,给地球的自我调节系统带来了额外的压力。在全球低碳经济背景下,我国坚持节能减排、增加森林蓄积量,提出了双碳目标,助力全球应对气候变化。

关键词: 深部碳循环, 固碳作用, 脱碳作用, 人为成因CO2排放

Abstract:

Carbon plays a fundamental role in subduction zones in melting enhancement, magma genesis and evolution, and petrological/thermodynamic processes in the deep Earth. The occurrence state of carbon in the deep Earth is controlled by temperature, depth (pressure), oxygen fugacity, and fluid property. When carbon of various occurrence states is transported to the deep Earth via subducting slab and then returns to the atmosphere through degassing, the so-called ‘deep carbon cycle’ is realized. Carbonation/decarbonation reactions are the main mechanisms affecting carbon transfer between the solid Earth, the atmosphere, and the oceans. Carbonation processes include silicate weathering, hydrothermal alteration, trench outer-rise serpentinization, organic carbon burial, and reverse weathering; while carbon transport is achieved by subduction of depositional and metasomatic sediments. Surface carbon, when transported to the Earth’s interior, may be retained within the subducting slab, transferred into the upper mantle wedge, or recycled into the deep Earth depending on the depth and redox state under specific tectonic settings; that carbon is then returned to the atmosphere via decarbonation mechanism through volcanic degassing, diffuse degassing in the forearc, dissolution, metamorphism, and melting to maintain a carbon balance at subduction zones. This systematic review summarizes the carbon occurrence states, carbon movements and change of carbon-bearing phases during carbon sequestration, transport, transfer, and degassing relevant to deep carbon cycling and the related carbon fluxes, analyzes the reasons for the inconsistencies in carbon-flux estimates, and discusses future research directions. Since the industrial revolution anthropogenic CO2 emission has contributed greatly to global warming, exerting extra pressure on Earth as a self-regulating system. In the context of transition to a low-carbon economy, China adheres to energy conservation, carbon emission reduction, and forest growth, and aims to peak CO2 emissions by 2030 and achieve carbon neutrality by 2060 to address the world climate crisis.

Key words: deep carbon cycle, carbonation, decarbonation, anthropogenic CO2 emissions

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