Abrupt Changes in Atmospheric Circulation During the Medieval Climate Anomaly and Little Ice Age Recorded by Sr‐Nd Isotopes in the Siple Dome Ice Core, Antarctica

The Southern Hemisphere westerly winds (SWW) play a critical role in global climate, yet their behavior on decadal to centennial timescales, and the mechanisms driving these changes during the preindustrial era, remain poorly understood. We present a decadally resolved record of dust compositions using strontium and neodymium isotope ratios in mineral dust from the Siple Dome ice core, Antarctica, to explore the potential that abrupt changes in SWW behavior occurred over the past millennium. The record spans portions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) intervals as defined in the Northern Hemisphere. We find evidence of an abrupt strengthening of atmospheric circulation during the MCA at ∼1125 CE (825 BP) that persisted for about 60 yr, indicating increased influence of Patagonia‐sourced dust. This occurs during an extended positive phase of Southern Annular Mode (SAM+)‐like conditions, characterized by high SWW velocities and a southerly shift of the main wind belt toward ∼60°S, suggesting that rapid changes in SWW strength could occur under the present SAM+ pattern. A second 20 yr long shift in dust compositions during the LIA at ∼1748 CE (200 BP) is coincident with higher dust delivery to Siple Dome, and may indicate increased dust emissions related to glacier activity in Patagonia. The new Siple Dome ice core data set demonstrates that Sr‐Nd isotopes can be used to trace shifts in atmospheric circulation on decadal timescales.

南半球西风带（SWW）在全球气候中起着关键作用，然而它们在十年到百年时间尺度上的行为，以及在前工业化时代驱动这些变化的机制，仍然知之甚少。我们利用来自南极西普尔穹顶冰芯的矿物粉尘中的锶和钕同位素比值，呈现了一份以十年为分辨率的粉尘成分记录，以探究过去千年中南半球西风带行为发生突变的可能性。该记录涵盖了北半球所定义的中世纪气候异常（MCA）和小冰期（LIA）时段的部分时间。我们发现，在公元1125年（距今825年）左右的中世纪气候异常期间，大气环流突然增强，持续了约60年，这表明来自巴塔哥尼亚的粉尘影响增加。这发生在类似南半球环状模（SAM +）正位相的延长阶段，其特征是南半球西风带速度较高，主风带向南移动至约南纬60°，这表明在当前的SAM +模式下，南半球西风带强度可能会发生快速变化。在公元1748年（距今200年）左右的小冰期期间，粉尘成分发生了第二次为期20年的变化，这与输送到西普尔穹顶的粉尘增多同时发生，可能表明巴塔哥尼亚的冰川活动导致粉尘排放增加。新的西普尔穹顶冰芯数据集表明，锶 - 钕同位素可用于追踪十年时间尺度上的大气环流变化。