New perspectives on deep carbon cycling  

作　　者：Weidong SUN 

机构地区：[1]Center of Deep Sea Research,Key Laboratory of Ocean Observation and Forecasting,Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China [2]Laoshan Laboratory,Qingdao 266237,China [3]University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Science China Earth Sciences》2024年第8期2411-2422,共12页中国科学（地球科学英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.92258303&42221005);the Marine S&T Fund of Shandong Province for The Laoshan Laboratory(Grant No.LSKJ202204100);the Major Basic Research Project of Shandong Province(Grant No.ZFJH202308);the Taishan Scholar Program of Shandong(Grant No.tspd20230609)。

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 CO_(2)and>2.6 bar of nitrogen.The protoatmosphere 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 CO_(2)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,Fe^(2+)undergoes disproportionation reactions,forming Fe^(3+)and metallic iron.Among these,Fe^(3+)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 Fe^(3+)ions and oxidizes diamond to carbonate,which under thermal disturbance

关 键 词：Carbon cycling Proto-atmosphere Amino acids Subduction initiation Passive margin subduction Atmospheric carbon dioxide 

分 类 号：P593[天文地球—地球化学]