Glacial expansion of oxygen-depleted seawater in the eastern tropical Pacific
Glacial expansion of oxygen-depleted seawater in the eastern tropical Pacific
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DOI：
10.1038/s41586-018-0589-x
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发表时间：
2018-10-18
期刊：
影响因子：
64.8
通讯作者：
Galbraith, Eric
中科院分区：
文献类型：
--
作者：
Hoogakker, Babette A. A.;Lu, Zunli;Galbraith, Eric
海洋中碳储存的增加被认为是解释冰河时期大气中二氧化碳浓度较低的一种机制;然而，这种储存的明确特征尚未发现（1）。在海水中，溶解气体氧气和二氧化碳通过有机物质的产生和衰变联系在一起，过去低氧浓度的重建表明生物介导的碳储存增加。海洋沉积物代用记录表明，在最后一个冰河时期，深海中的氧浓度确实较低，但太平洋的近表层和中层沃茨-其中大部分目前氧含量很低-在冰河时期氧含量一般较好（1-3）。这种垂直对立可能表明碳储存的净流域综合变化最小。在这里，我们应用了一种双重代理方法，结合定性的上层水柱和定量的底层水氧气重建（4）（，5），以限制自上一个冰河时代以来热带太平洋东部低氧沃茨垂直范围的变化。我们的串联代理重建提供了证据，在最后一次冰期在东太平洋的氧气消耗的向下扩张，没有迹象表明更大的氧化在上游的水柱。我们外推我们的定量深水氧重建表明，太平洋冰川的呼吸碳库大幅增加，建立它作为耦合机制的重要组成部分，导致低水平的大气二氧化碳在冰川。
Increased storage of carbon in the oceans has been proposed as a mechanism to explain lower concentrations of atmospheric carbon dioxide during ice ages; however, unequivocal signatures of this storage have not been found(1). In seawater, the dissolved gases oxygen and carbon dioxide are linked via the production and decay of organic material, with reconstructions of low oxygen concentrations in the past indicating an increase in biologically mediated carbon storage. Marine sediment proxy records have suggested that oxygen concentrations in the deep ocean were indeed lower during the last ice age, but that near-surface and intermediate waters of the Pacific Ocean-a large fraction of which are poorly oxygenated at present-were generally better oxygenated during the glacial(1-3). This vertical opposition could suggest a minimal net basin-integrated change in carbon storage. Here we apply a dual-proxy approach, incorporating qualitative upper-water-column and quantitative bottom-water oxygen reconstructions(4)(,5), to constrain changes in the vertical extent of low-oxygen waters in the eastern tropical Pacific since the last ice age. Our tandem proxy reconstructions provide evidence of a downward expansion of oxygen depletion in the eastern Pacific during the last glacial, with no indication of greater oxygenation in the upper reaches of the water column. We extrapolate our quantitative deep-water oxygen reconstructions to show that the respired carbon reservoir of the glacial Pacific was substantially increased, establishing it as an important component of the coupled mechanism that led to low levels of atmospheric carbon dioxide during the glacial.