Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697.
Department of Earth System Science, University of California, Irvine, CA 92697.
Proc Natl Acad Sci U S A. 2020 Sep 15;117(37):22866-22872. doi: 10.1073/pnas.2004986117. Epub 2020 Aug 31.
Climate-driven depletion of ocean oxygen strongly impacts the global cycles of carbon and nutrients as well as the survival of many animal species. One of the main uncertainties in predicting changes to marine oxygen levels is the regulation of the biological respiration demand associated with the biological pump. Derived from the Redfield ratio, the molar ratio of oxygen to organic carbon consumed during respiration (i.e., the respiration quotient, [Formula: see text]) is consistently assumed constant but rarely, if ever, measured. Using a prognostic Earth system model, we show that a 0.1 increase in the respiration quotient from 1.0 leads to a 2.3% decline in global oxygen, a large expansion of low-oxygen zones, additional water column denitrification of 38 Tg N/y, and the loss of fixed nitrogen and carbon production in the ocean. We then present direct chemical measurements of [Formula: see text] using a Pacific Ocean meridional transect crossing all major surface biome types. The observed [Formula: see text] has a positive correlation with temperature, and regional mean values differ significantly from Redfield proportions. Finally, an independent global inverse model analysis constrained with nutrients, oxygen, and carbon concentrations supports a positive temperature dependence of [Formula: see text] in exported organic matter. We provide evidence against the common assumption of a static biological link between the respiration of organic carbon and the consumption of oxygen. Furthermore, the model simulations suggest that a changing respiration quotient will impact multiple biogeochemical cycles and that future warming can lead to more intense deoxygenation than previously anticipated.
气候变化导致海洋氧气枯竭，这强烈影响了全球碳和营养物质的循环以及许多动物物种的生存。在预测海洋氧气水平变化时，主要的不确定性之一是与生物泵相关的生物呼吸需求的调节。呼吸商（[Formula: see text]）是由 Redfield 比值推导出来的，它是呼吸过程中消耗的氧气与有机碳的摩尔比（即呼吸商），通常假设为常数，但很少有实际测量值。我们使用一个预测地球系统模型表明，呼吸商从 1.0 增加 0.1，会导致全球氧气减少 2.3%，低氧区大幅扩张，水柱脱氮量增加 38Tg N/y，以及海洋中固定氮和碳的损失。然后，我们利用一个跨越所有主要表层生物群系类型的太平洋南北向断面，直接对[Formula: see text]进行了化学测量。观测到的[Formula: see text]与温度呈正相关，区域平均值与 Redfield 比例有显著差异。最后，一个用营养物质、氧气和碳浓度约束的独立全球逆模式分析支持了输出有机物质中[Formula: see text]与温度之间的正相关性。我们的研究结果提供了证据，证明了在有机碳呼吸和氧气消耗之间存在静态生物联系的常见假设是不正确的。此外，模型模拟表明，呼吸商的变化将影响多个生物地球化学循环，并且未来的变暖可能导致比以前预期更严重的缺氧。
