New index of ferromanganese crusts reflecting oceanic environmental oxidation  

作　　者：WU GuangHai ZHOU HuaiYang ZHANG HaiSheng LING HongFei MA WeiLin ZHAO HongQiao CHEN JianLin LIU JieHong 

机构地区：[1]Key Laboratory of Marine Ecosystem&Biogeochemistry of State Oceanic Administration,Hangzhou 310012,China [2]Key Laboratory of Submarine Geoscience of State Oceanic Administration,Hangzhou 310012,China [3]Geochemistry Institute of Guangzhou,Chinese Academy of Sciences,Guangzhou 510640,China [4]State Key Laboratory for Mineral Deposit Research,Nanjing University,Nanjing 210093,China

出　　处：《Science China Earth Sciences》2007年第3期371-384,共14页中国科学（地球科学英文版）

基　　金：the National Natural Science Foundation of China (Grant No. 40206010);the National Key Basic Research Program of China (Grant No. G2000078503);the Young People Marine Science Foundation of State Oceanic Administration (Grant No. 2002316);the Open Foundation of State Key Labora-tory for Mineral Deposit Research at Nanjing University

摘　　要：Ferromanganese crusts (hereinafter crusts) form in aerobic environment and the environmental oxida-tion degree is recorded by the redox sensitive element Co in the crusts. The ages of the layers from the surface to bottom of the crusts are determined, and main element contents at high resolution along the depth sections of three crusts from the Pacific Ocean are analyzed by an electron microprobe. Thus the variations of Co/(Fe+Mn) and Co/(Ni+Cu) with age/depth of the crust layers are obtained. By comparing the ratios of Co/(Fe+Mn) and Co/(Ni+Cu) with the δ 18O curves of the Pacific benthic foraminifera, we find that these two ratios can reflect the variation of the environmental oxidation state under which the crust layers deposit. The evolution of the oxidation degree reflected by the two indexes resembles the evo-lution of temperature since the Oligocene reflected by the δ 18O curves of the Pacific benthic foraminif-era. This suggests that the crust-forming environment after the Oligocene is controlled mainly by the oxygen-rich bottom water originated from the Antarctic bottom water (AABW). However it is not the case prior to the Oligocene. Furthermore it suggests that the environmental oxidation degree controls the formation of the crusts and the Co contents in the crusts. This explains why the Co contents in the crusts increase with time up to now.Ferromanganese crusts (hereinafter crusts) form in aerobic environment and the environmental oxidation degree is recorded by the redox sensitive element Co in the crusts. The ages of the layers from the surface to bottom of the crusts are determined, and main element contents at high resolution along the depth sections of three crusts from the Pacific Ocean are analyzed by an electron microprobe. Thus the variations of Co/(Fe+Mn) and Co/(Ni+Cu) with age/depth of the crust layers are obtained. By comparing the ratios of Co/(Fe+Mn) and Co/(Ni+Cu) with the δ 18O curves of the Pacific benthic foraminifera, we find that these two ratios can reflect the variation of the environmental oxidation state under which the crust layers deposit. The evolution of the oxidation degree reflected by the two indexes resembles the evolution of temperature since the Oligocene reflected by the δ 18O curves of the Pacific benthic foraminifera. This suggests that the crust-forming environment after the Oligocene is controlled mainly by the oxygen-rich bottom water originated from the Antarctic bottom water (AABW). However it is not the case prior to the Oligocene. Furthermore it suggests that the environmental oxidation degree controls the formation of the crusts and the Co contents in the crusts. This explains why the Co contents in the crusts increase with time up to now.

关 键 词：FERROMANGANESE CRUSTS the PACIFIC Ocean OXIDATION degree of environment the OLIGOCENE AABW 

分 类 号：P744.3[天文地球—海洋科学]