Mechanisms of Low‐Frequency Oxygen Variability in the North Pacific
Mechanisms of Low‐Frequency Oxygen Variability in the North Pacific
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DOI：
10.1029/2018gb005987
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发表时间：
2019-02
影响因子：
5.2
通讯作者：
T. Ito;M. Long;C. Deutsch;S. Minobe;Daoxun Sun
中科院分区：
文献类型：
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作者：
T. Ito;M. Long;C. Deutsch;S. Minobe;Daoxun Sun
利用历史观测资料和群落地球系统模式的后验模拟，研究了北太平洋溶解氧（O2）年际和年代际变化的机制。模拟的上层海洋（200 m） O2的变率与采样密度较高的观测值有中等相关性。O2变异的优势模态解释了24.8%的变异，与太平洋年代际涛动（PDO）指数呈显著相关（r = 0.68）。PDO控制上层海洋氧变率的两个主要机制被假设。等压线的垂直运动（“隆起”）驱动了热带深处的氧变化；在PDO正相位（El Niño‐like）下，东热带等环流面被压制，导致上层水柱的O2增加。与热带不同，俯冲的变化是控制温带外氧变率的主要因素。这些假设是通过对比O2异常与由潜在密度异常计算的波动引起的变异性分量来检验的。等环流起伏是热带地区O2变异性的主要控制因素，但起伏本身并不能完全解释热带O2变异性的幅度，可能表明生物O2消耗的强化变化。中纬度O2变率确实反映了俯冲区下游的海洋通气，其中O2异常与冬季混合层深度相关。这些机制与PDO同步，产生了一个盆地尺度的O2变化模式，其量级与本世纪“不受控制”排放情景下海洋脱氧的预估速率相当。
This study investigates the mechanisms of interannual and decadal variability of dissolved oxygen (O2) in the North Pacific using historical observations and a hindcast simulation using the Community Earth System Model. The simulated variability of upper ocean (200 m) O2 is moderately correlated with observations where sampling density is relatively high. The dominant mode of O2 variability explains 24.8% of the variance and is significantly correlated with the Pacific Decadal Oscillation (PDO) index (r = 0.68). Two primary mechanisms are hypothesized by which the PDO controls upper ocean O2 variability. Vertical movement of isopycnals (“heave”) drives O2 variations in the deep tropics; isopycnal surfaces are depressed in the eastern tropics under the positive (El Niño‐like) phase of PDO, leading to O2 increases in the upper water column. In contrast to the tropics, changes in subduction are the primary control on extratropical O2 variability. These hypotheses are tested by contrasting O2 anomalies with the heave‐induced component of variability calculated from potential density anomalies. Isopycnal heave is the leading control on O2 variability in the tropics, but heave alone cannot fully explain the amplitude of tropical O2 variability, likely indicating reinforcing changes from the biological O2 consumption. Midlatitude O2 variability indeed reflects ocean ventilation downstream of the subduction region where O2 anomalies are correlated with the depth of winter mixed layer. These mechanisms, synchronized with the PDO, yield a basin‐scale pattern of O2 variability that are comparable in magnitude to the projected rates of ocean deoxygenation in this century under “unchecked” emission scenario.