In contrast to the modern-day climate, North Pacific deep water formation and a Pacific meridional overturning circulation (PMOC) may have been active during past climate conditions, in particular during the Pliocene epoch (some 3–5 million years ago). Here, we use a climate model simulation with a robust PMOC cell to investigate the pathways of the North Pacific deep water from subduction to upwelling, as revealed by Lagrangian particle trajectories. We find that similar to the present-day Atlantic Meridional Overturning Circulation (AMOC), most subducted North Pacific deep water upwells in the Southern Ocean. However, roughly 15% upwells in the tropical Indo-Pacific Oceans instead—a key feature distinguishing the PMOC from the AMOC. The connection to the Indian Ocean is relatively fast, at about 250 years. The connection to the tropical Pacific is slower (∼800 years) as water first travels to the subtropical South Pacific then gradually upwells through the thermocline.

中文翻译：

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活跃的太平洋子午向翻转环流（PMOC）的海洋路径

与现代气候相反，在过去的气候条件下，特别是在上新世时期（大约3-5百万年前），北太平洋深水形成和太平洋子午翻转环流（PMOC）可能一直活跃。在这里，我们使用具有强大PMOC单元的气候模型模拟来研究北太平洋深水从俯冲到上升流的路径，这是由拉格朗日粒子轨迹揭示的。我们发现，与当今的大西洋子午线翻转环流（AMOC）类似，大多数俯冲的南太平洋北太平洋深水上升流。但是，在热带印度洋-太平洋中上升幅度约为15％，这是PMOC与AMOC区别的一个关键特征。与印度洋的连接相对较快，大约需要250年。