据介绍，大量的代用记录表明，末次盛冰期（LGM，约 21,000年前）大西洋经向翻转环流（AMOC）发生了深刻的重组，北大西洋深水（NADW）相对于现在（PD）明显变浅，并形成了冰川北大西洋中间水（GNAIW）。然而，几乎所有以前的观测和模拟研究都集中在纬向平均二维AMOC特征上，而最近对现代AMOC理解的进展，揭示了一个更复杂的三维结构，NADW通过不同的途径从北大西洋亚极地渗透到低纬度地区。
本研究结合231Pa/230Th数据重建和模型模拟，揭示了冰川AMOC三维结构的显著变化。具体而言，位于大西洋中脊以东的中纬度东部路径（EP）在LGM期间经历了显著的增强，该路径将近一半的北大西洋深水从亚极地环流输送到副热带环流。与PD时的NADW相比，更大部分的GNAIW在LGM期间被输送到东部盆地，导致LGM期间东部和西部盆地的231Pa/230Th变化相反。
此外，与EP在PD的风向控制机制相反，末次盛冰期中纬度东部路径的增强，主要是由北大西洋副极地上的开阔海洋，对流（海盆尺度）所作用的边缘流引起的。研究结果强调了计算三维海洋学变化的重要性，以实现更准确地重建过去的AMOC。
附：英文原文
Title: Open ocean convection drives enhanced eastern pathway of the Glacial Atlantic Meridional Overturning Circulation
Author: Gu, Sifan, Liu, Zhengyu, Ng, Hong Chin, Lynch-Stieglitz, Jean, McManus, Jerry F., Spall, Michael, Jahn, Alexandra, He, Chengfei, Li, Lingwei, Yan, Mi, Wu, Lixin
Issue&Volume: 2024-10-29
Abstract: Abundant proxy records suggest a profound reorganization of the Atlantic Meridional Overturning Circulation (AMOC) during the Last Glacial Maximum (LGM, ~21,000 y ago), with the North Atlantic Deep Water (NADW) shoaling significantly relative to the present-day (PD) and forming Glacial North Atlantic Intermediate Water (GNAIW). However, almost all previous observational and modeling studies have focused on the zonal mean two-dimensional AMOC feature, while recent progress in the understanding of modern AMOC reveals a more complicated three-dimensional structure, with NADW penetrating from the subpolar North Atlantic to lower latitude through different pathways. Here, combining 231Pa/230Th reconstructions and model simulations, we uncover a significant change in the three-dimensional structure of the glacial AMOC. Specifically, the mid-latitude eastern pathway (EP), located east of the Mid-Atlantic Ridge and transporting about half of the PD NADW from the subpolar gyre to the subtropical gyre, experienced substantial intensification during the LGM. A greater portion of the GNAIW was transported in the eastern basin during the LGM compared to NADW at the PD, resulting in opposite 231Pa/230Th changes between eastern and western basins during the LGM. Furthermore, in contrast to the wind-steering mechanism of EP at PD, the intensified LGM EP was caused primarily by the rim current forced by the basin-scale open-ocean convection over the subpolar North Atlantic. Our results underscore the importance of accounting for three-dimensional oceanographic changes to achieve more accurate reconstructions of past AMOC.
DOI: 10.1073/pnas.2405051121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2405051121