New perspectives on deep carbon cycling

doi:10.1007/s11430-024-1364-0

	New perspectives on deep carbon cycling
	Sun, Weidong1,2,3
	2024-08-01
发表期刊	SCIENCE CHINA-EARTH SCIENCES
ISSN	1674-7313
卷号	67 期号:8 页码:2563-2582
通讯作者	Sun, Weidong([email protected])
摘要	The proto-atmosphere serves as a crucial starting point for the carbon cycle. Estimations based on atmospheric data from Mars and Venus suggest that Earth's proto-atmosphere contained >110 bar of CO2 and >2.6 bar of nitrogen. The proto-atmosphere had over 1000 bar of water vapor during the magma ocean stage, assuming the proto-ocean had a volume of two oceans of water. During this stage both water and carbon dioxide were in a supercritical state at the magma-atmosphere interface. Intense serpentinization reactions occurred due to rock-water interaction, producing abundant hydrogen. Consequently, nitrogen is reduced to ammonia, and carbon dioxide to methane, forming carbonate simultaneously. The proto-atmosphere dominated by methane, ammonia, and hydrogen formed a significant amount of amino acids through lightning. This process is essential not only to the origin of life, but also to the early carbon-nitrogen cycle on Earth. By the Hadean eon, a large amount of CO2 was sequestered as carbonate and organic material. Subsequently, it mainly entered the deep mantle through mantle overturn or subduction. In the mantle transition zone, carbonate undergoes "Redox freezing", where carbonate is reduced to diamond through oxidation of ferrous iron in the melt. In the lower mantle, Fe2+ undergoes disproportionation reactions, forming Fe3+ and metallic iron. Among these, Fe3+ mainly resides in bridgmanite, thereby increasing the oxygen fugacity of the lower mantle, while metallic iron falls to the Earth's core. The distribution of carbon in the mantle is crucial for deep carbon cycling. The density curves of diamond and mantle peridotite melt intersect at the bottom of the mantle transition zone (about 660 km). This density crossover leads to the accumulation of diamond during the magma ocean stage. When materials such as subducting slabs enter the lower mantle, compensatory upwelling of lower mantle material occurs. Bridgmanite enters the upper mantle, decomposes, releasing Fe3+ ions and oxidizes diamond to carbonate, which under thermal disturbance from kimberlite and igneous carbonatites, moves upward. This carbonate layer may have caused significant topographic fluctuations at the 660 km boundary. Currently, diamond in this layer may still not have been completely oxidized to carbonate or carbon dioxide, serving as a redox buffering layer. This is a key factor in constraining deep carbon cycling. Subduction zones are important pathways for facilitating the cycling. Processes in the Earth's deep carbon cycle significantly influence the carbon content of surface reservoirs. The fluctuations in atmospheric CO2 content since the Neogene are closely linked to the uplift of the Tibetan Plateau and the subduction of the western Pacific Plate. Around 60 million years ago, the closure of the Neo-Tethys Ocean led to subduction of the Indian passive margin. The massive sediments on the Indian margin carried down large amounts of carbonate and organic material into the mantle, and the resulting volcanism released large amounts of greenhouse gases such as CO2 and methane into the atmosphere. The subduction of the Neo-Tethys Ocean passive margin weakened at about 51 Ma, and subduction of the western Pacific began. The depth of the western Pacific Ocean generally exceeds the carbonate compensation depth, and the amount of carbonate carried by subducting oceanic crust is minimal. Consequently, the input of subducted carbonate decreased significantly, leading to a substantial reduction in CO2 emissions from volcanoes. Based on volcanic data from the past 12,000 years, the average rate of volcanic eruptions in subduction zones is estimated to be about 3 cubic kilometers per year. The weathering rate of volcanic ash is much higher than that of continental crust materials such as granite. The calcium, magnesium, and other ions provided by weathering of global volcanic ash are equivalent to the flux of global rivers into the oceans. The increase in volcanic ash and the decrease in CO2 emissions from subduction zones have led to a decrease in atmospheric CO2 levels, which is a key factor in the sustained global cooling since 51 million years ago.
关键词	Carbon cycling Proto-atmosphere Amino acids Subduction initiation Passive margin subduction Atmospheric carbon dioxide
DOI	10.1007/s11430-024-1364-0
收录类别	SCI
语种	英语
资助项目	National Natural Science Foundation of China[92258303]; National Natural Science Foundation of China[42221005]; Marine S&T Fund of Shandong Province for The Laoshan Laboratory[LSKJ202204100]; Major Basic Research Project of Shandong Province[ZFJH202308]; Taishan Scholar Program of Shandong[tspd20230609]
WOS研究方向	Geology
WOS类目	Geosciences, Multidisciplinary
WOS记录号	WOS:001269979900003
出版者	SCIENCE PRESS
WOS关键词	NORTH CHINA CRATON ; NB-FE DEPOSIT ; OXIDATION-STATE ; EXPERIMENTAL SERPENTINIZATION ; WEATHERING RATES ; SUBDUCTION ZONES ; INNER-MONGOLIA ; FORE-ARC ; MANTLE ; INDIA
引用统计
文献类型	期刊论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/186273
专题	深海极端环境与生命过程研究中心海洋环流与波动重点实验室
通讯作者	Sun, Weidong
作者单位	1.Chinese Acad Sci, Inst Oceanol, Ctr Deep Sea Res, Key Lab Ocean Observat & Forecasting, Qingdao 266071, Peoples R China 2.Laoshan Lab, Qingdao 266237, Peoples R China 3.Univ Chinese Acad Sci, Beijing 100049, Peoples R China
第一作者单位	深海极端环境与生命过程研究中心
通讯作者单位	深海极端环境与生命过程研究中心
推荐引用方式 GB/T 7714	Sun, Weidong. New perspectives on deep carbon cycling[J]. SCIENCE CHINA-EARTH SCIENCES,2024,67(8):2563-2582.
APA	Sun, Weidong.(2024).New perspectives on deep carbon cycling.SCIENCE CHINA-EARTH SCIENCES,67(8),2563-2582.
MLA	Sun, Weidong."New perspectives on deep carbon cycling".SCIENCE CHINA-EARTH SCIENCES 67.8(2024):2563-2582.