Zhang Shanwu, Qiu Fuwen, Chen Hangyu, Jing Chunsheng
Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, 361005, China.
Fujian Provincial Key Laboratory of Marine Physical and Geological Processes, Xiamen, 361005, China.
Sci Rep. 2025 Jul 11;15(1):25117. doi: 10.1038/s41598-025-09749-7.
Deep overflows across the saddles on the Ninetyeast Ridge are vital for sustaining the deep limb of the Indian Ocean meridional overturning circulation. However, the volume transport or temporal variability of these overflows remains largely unknown. Through a 17-month moored record of velocity profiles, the time-averaged volume transport of the overflow across the saddle near 10°S is estimated at 1.3 Sv (1 Sv = 1 × 10 m/s), with a 95% confidence interval of 0.8-1.6 Sv. The estimated volume transport is close to those values determined from rotating hydraulic theory and early hydrographic observations. The overflow transport exhibits significant variabilities at semiannual (170 days) and intraseasonal (73 days) scales, which are closely correlated with the wind stress curl east of the Ninetyeast Ridge. These variabilities are attributed to vertically propagating Rossby waves originating from wind stress curl-induced Ekman pumping, which is demonstrated via spectral empirical orthogonal function decomposition of numerical model outputs and by ray tracing based on the dispersion relation for baroclinic Rossby waves. This finding highlights that wind-driven variability plays a crucial role in modulating deep currents and associated overflows in the southeast Indian Ocean.
穿越九十东脊鞍部的深层溢流对于维持印度洋经向翻转环流的深层分支至关重要。然而，这些溢流的体积输送量或时间变化性在很大程度上仍不为人知。通过对流速剖面进行为期17个月的锚定记录，估算出在南纬10°附近鞍部的溢流时间平均体积输送量为1.3 西弗（1西弗 = 1×10⁶ 立方米/秒），95%置信区间为0.8 - 1.6西弗。估算出的体积输送量与根据旋转水力学理论和早期水文观测确定的值相近。溢流输送量在半年（170天）和季节内（73天）尺度上表现出显著变化，这与九十东脊以东的风应力旋度密切相关。这些变化归因于由风应力旋度引起的埃克曼抽吸所产生的垂直传播罗斯贝波，这通过数值模型输出的谱经验正交函数分解以及基于斜压罗斯贝波频散关系的射线追踪得以证明。这一发现突出表明，风驱动的变化性在调节印度洋东南部的深层洋流及相关溢流方面起着关键作用。
