Ferromanganese crusts as recorders of marine dissolved oxygen
Ferromanganese crusts as recorders of marine dissolved oxygen
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DOI：
10.1016/j.epsl.2019.116057
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发表时间：
2020-03
影响因子：
5.3
通讯作者：
Kevin M. Sutherland;J. Wostbrock;C. Hansel;Z. Sharp;J. Hein;S. Wankel
中科院分区：
文献类型：
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作者：
Kevin M. Sutherland;J. Wostbrock;C. Hansel;Z. Sharp;J. Hein;S. Wankel
对流层O2相对于海水的独特的三重氧同位素组成是地球化学反应（如初级生产力、呼吸作用）、与平流层交换以及不同含氧储层（即O2、O3和CO2）的相对大小的结果。这种同位素组成的差异使对流层O2可以作为地球化学和大气过程的记录，也可以用于确定对流层氧的同位素指纹在岩石记录中的位置。在以前的研究中，对流层氧的同位素记录在很大程度上限于分析大陆冰川中捕获的气体和其他代理物的拼凑，最值得注意的是硫酸盐的三重氧特征。在这里，我们表明，最上层的水成，深海铁锰结壳从每个主要的海洋盆地有一个三重氧同位素组成与溶解氧的直接合并一致。铁锰结壳中δ 18 O和Δ′ 17 O的变化表明，锰氧化物端元中含有近50：50的水氧和溶解氧的混合物。我们的数据表明，这种信号也持续到地壳的较老层，可能保存近7 500万年的低对流层的氧同位素组成和随后的深海呼吸。我们的分析的氧同位素值，散装化学，并估计当地溶解氧地壳顶部样品显示，散装化学的变化最终表现出更多的影响比溶解氧的变化对氧质量平衡，提出了一个挑战，明确确定当地溶解氧。虽然分析方面的挑战依然存在，但这些分布广泛的层状铁锰结壳矿床可能为今后探究数百万年前对流层和深海氧循环的历史或相对历史提供一条可行的途径。
The distinct triple oxygen isotope composition of tropospheric O 2 relative to seawater is the result of biogeochemical reactions (eg primary productivity, respiration), exchange with the stratosphere, and the relative size of different oxygen-containing reservoirs, namely O 2, O 3, and CO 2. This difference in isotopic composition gives tropospheric O 2 utility as a record of biogeochemical and atmospheric processes and may also be used for determining where in the rock record isotopic fingerprints of tropospheric oxygen may be preserved. The isotopic record of tropospheric oxygen in previous studies is largely limited to analyses of gas trapped in continental glaciers and a patchwork of other proxies, most notably the triple oxygen signature of sulfate. Here we show the uppermost layers of hydrogenetic, deep-ocean ferromanganese crusts from each of the major ocean basins have a triple oxygen isotope composition consistent with the direct incorporation of dissolved oxygen. The range of δ 18 O and Δ′ 17 O in ferromanganese crusts suggests the Mn oxide endmember contains a near 50: 50 mixture of oxygen from water and dissolved O 2. Our data indicate this signal also persists into older layers of the crusts, potentially preserving near 75 million years of the oxygen isotopic composition of the lower troposphere and subsequent deep-ocean respiration. Our analysis of oxygen isotope values, bulk chemistry, and estimated local dissolved oxygen for crust top samples reveals that variations in bulk chemistry ultimately exhibit more influence on the oxygen mass balance than changes in dissolved oxygen, presenting a challenge for unambiguous determination of local dissolved oxygen. Although analytical challenges remain, these widespread, layered deposits of ferromanganese crust may offer a viable path for future interrogation of the history or relative history of the oxygen cycle of the troposphere and deep ocean millions of years into the past.