Abstract The South American summer monsoon (SASM) is the most important climate system of tropical South America, transporting moisture from the tropical Atlantic Ocean to the core of the continent during the austral summer. Recent paleoclimate studies suggest that past variability of the SASM has been more heterogenous in space and time than previously thought, implying that different atmospheric drivers controlled its long-term evolution. Unfortunately, past SASM reconstructions are largely limited to the last 2000 years and mainly focused on the core of the monsoon domain where precipitation does not fall exclusively during the monsoon season, thereby limiting our understanding of its long-term changes, drivers and mechanisms. Here we present a new 4000-year SASM precipitation reconstruction based on a high-resolution pollen sequence from a mountain lake in the dry Andes of northern Chile (21°S). We provide evidence for two centennial-scale intervals of enhanced SASM precipitation between 4000–3400 and 2300-1900 cal yr BP. These intervals are replicated in records from the southern portion of the central Andes (>18°S) but not clearly detected further north, suggesting the existence of a monsoon dynamics largely decoupled from latitudinal shifts of the Intertropical Convergence Zone. A comparison with precipitation reconstructions from the entire SASM domain and modern climate datasets suggests a teleconnection with the Southern Hemisphere circulation through the intensification of the South Atlantic Convergence Zone and/or the intrusion of extra-tropical Atlantic moisture. Our results highlight that significant spatial and temporal variability of the SASM occurred during the most recent millennia, and therefore social and environmental forecast should consider that similar variations will likely occur in the future.

中文翻译：

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南美夏季风的全新世晚期动力学：来自智利北部安第斯山脉（21°S）的新见解

摘要 南美夏季风（SASM）是南美洲热带地区最重要的气候系统，在南方夏季将水分从热带大西洋输送到大陆核心。最近的古气候研究表明，SASM 过去的变化在空间和时间上比以前认为的更加异质，这意味着不同的大气驱动因素控制了它的长期演变。不幸的是，过去的 SASM 重建主要限于最近 2000 年，并且主要集中在季风域的核心，其中降水并不完全在季风季节下降，从而限制了我们对其长期变化、驱动因素和机制的理解。在这里，我们基于智利北部干燥的安第斯山脉 (21°S) 的高山湖泊的高分辨率花粉序列，展示了一个新的 4000 年 SASM 降水重建。我们提供了 4000-3400 和 2300-1900 cal BP 之间两个百年尺度的 SASM 降水增强间隔的证据。这些间隔在安第斯山脉中部南部（> 18°S）的记录中重复，但在更北的地方没有清楚地检测到，这表明季风动力学的存在很大程度上与热带辐合带的纬度变化脱钩。与整个 SASM 域的降水重建和现代气候数据集的比较表明，通过南大西洋辐合带的强化和/或热带大西洋水分的侵入，与南半球环流存在遥相关。我们的结果强调了 SASM 的显着时空变异发生在最近的几千年中，因此社会和环境预测应该考虑到未来可能会发生类似的变化。