The Lyell Centre, Heriot-Watt University, Edinburgh, UK.
Department of Earth Sciences, University of Oxford, Oxford, UK.
Nature. 2018 Oct;562(7727):410-413. doi: 10.1038/s41586-018-0589-x. Epub 2018 Oct 17.
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. 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. 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, 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.
海洋中碳的储存增加被认为是解释冰期大气二氧化碳浓度降低的一种机制;然而，这种储存的明确特征尚未被发现。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减而相互关联，过去低氧浓度的重建表明生物介导的碳储存增加。海洋沉积物示踪剂记录表明，在上一个冰期，深海中的氧气浓度确实较低，但太平洋的近表层和中层水——其中很大一部分目前氧气含量较低——在冰期通常氧气含量较高。这种垂直的对立可能表明碳储存的净盆地综合变化最小。在这里，我们应用了一种双重示踪剂方法，结合定性的上层水柱和定量的底层水氧重建，来约束自上一个冰期以来东热带太平洋低氧水垂直范围的变化。我们的串联示踪剂重建提供了证据，表明在上一个冰期，东太平洋的氧气消耗向下扩展，水柱上层没有氧气增加的迹象。我们推断我们的定量深海氧重建，以显示呼吸碳库的冰期太平洋大大增加，建立它作为一个重要的组成部分的耦合机制，导致大气中的二氧化碳浓度在冰期较低。
