Both deepwater formation and the obduction processes converting dense deep water to lighter surface water are the engine for the global meridional overturning circulation (MOC). Their spatio‐temporal variations effectively modify the ocean circulation and related carbon cycle, which affects climate evolution throughout geological time. Using early‐Eocene bathymetry and enhanced atmospheric CO₂ concentration, the IPSL‐CM5A2 climate model has simulated a well‐ventilated Southern Ocean associated with a strong anticlockwise MOC. To trace the fates of these paleo‐Antarctic Bottom Water (paleo‐AABW), we conducted Lagrangian analyses using these IPSL‐CM5A2 model results and tracking virtual particles released at the lower limb of the MOC, defined as an initial section at 60°S below 1,900 m depth. Diagnostic analysis of these particles trajectories reveals that most paleo‐AABW circulates back to the Southern Ocean through either the initial section (43%) or the section above (31%), the remaining (>25%) crossing the base of the mixed layer mostly in tropical regions (up to half). The majority of water parcels ending in the mixed layer experience negative density transformations, intensified in the upper 500 m and mostly occurring in tropical upwelling regions, with a spatial pattern consistent with the wind‐driven Ekman pumping, largely determined by the Eocene wind stress and continental geometry. In the same way as present‐day North Atlantic Deep Water upwells in the Southern Ocean, our results suggest that the strong tropical and equatorial upwelling during the Eocene provides an efficient pathway from the abyss to the surface, but at much higher temperature, with potential implications for the oceanic carbon cycle.

中文翻译：

---

始新世早期古南极水的命运：基于对IPSL-CM5A2气候模型模拟的拉格朗日分析

深水的形成和将稠密的深水转化为较轻的地表水的引诱过程，都是全球经向翻转循环（MOC）的引擎。它们的时空变化有效地改变了海洋环流和相关的碳循环，从而影响了整个地质时期的气候演变。使用早期始新世测深法和增强的大气CO ₂IPSL‐CM5A2气候模式模拟了一个通风良好的南大洋，并伴有强烈的逆时针MOC。为了追踪这些古南极底水的命运，我们使用这些IPSL-CM5A2模型结果进行了拉格朗日分析，并跟踪了在MOC下肢释放的虚拟颗粒，定义为60°S的初始剖面深度小于1,900 m。对这些粒子轨迹的诊断分析表明，大多数古AABW通过初始剖面（43％）或以上剖面（31％）循环返回南大洋，其余（> 25％）穿过混合层的底部大部分在热带地区（最多一半）。以混合层结尾的大多数水包都经历负密度转换，在上部500 m强度增强，主要发生在热带上升区，其空间格局与风驱动的埃克曼抽水相一致，这在很大程度上取决于始新世的风应力和大陆几何。与当今南大西洋北部大西洋深水上升流的方式相同，我们的结果表明，始新世期间强烈的热带和赤道上升流提供了从深渊到地表的有效途径，但是在更高的温度下具有潜在的对海洋碳循环的影响。