Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends
Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends
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DOI：
10.5194/bg-12-5429-2015
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发表时间：
2015-01-01
期刊：
影响因子：
4.9
通讯作者：
Bianchi, D.
中科院分区：
文献类型：
--
作者：
Cabre, A.;Marinov, I.;Bianchi, D.
我们分析了11个地球系统模式对耦合模式比较项目第五阶段贡献的太平洋氧气最小区(OMZ)的模拟，重点是平均状态和气候变化预测。这些模拟往往高估了OMZ的体积，特别是在热带和南半球。与观测结果相比，由于中间水团通风的半球间偏差，五个模型在氧气分布上引入了不正确的经向不对称，包括较大的南部OMZ和较弱的北部OMZ。与观测结果相比，七个模型显示了热带低氧的程度太深，源于上层赤道通风不足，加上生物驱动的深部颗粒有机碳向下通量太大，由真光层输出的粒子太高，以及上层的再矿化太弱。在年际尺度上，东太平洋OMZ的氧气动态由生物消耗主导，并与Walker环流中的自然变化有关。然而，在气候变化情景RCP8.5下，所有模拟都产生了到21世纪末热带太平洋中深处氧浓度的小而不同的变化，这是由于与变暖有关的氧饱和度下降和生物氧利用下降之间几乎完美的补偿。气候变化预测与最近的观测结果不一致，这些观测显示热带太平洋中深处的氧气水平正在下降。在OMZ中，所有的CMIP5模型都预测，由于通风总体放缓和气温上升，低纬度大部分表层和深海以及高纬度所有深度的氧气将减少。
We analyse simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean, combined with too large a biologically driven downward flux of particulate organic carbon at depth, caused by particle export from the euphotic layer that is too high and remineralization in the upper ocean that is too weak.At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific.Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface and deep ocean at low latitudes and over all depths at high latitudes due to an overall slow-down of ventilation and increased temperature.