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 similar to 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 similar to 60 degrees 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 similar to 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. Plain Language Summary The prevailing winds that encircle Antarctica, blowing west to east, play an outsized role in global climate. Because they blow continuously over the ocean, they create ocean currents and cause upwelling. When deep ocean water comes to the surface, it releases carbon dioxide into the atmosphere, causing the climate to warm. Changes in wind strength and positioning modulate the release of carbon dioxide. Therefore, knowing how and why the winds shift is important for understanding how Earth's climate system operates. We use the composition of dust preserved in an Antarctic ice core to learn how the balance of dust sources changed during the past millennium. This allows us to track past shifts in the winds around Antarctica and to learn how they respond to climate changes on short timespans, such as decades to centuries. We observe an abrupt change in dust composition at similar to 1125 CE lasting for about 60 yr, indicating a greater influence of dust sourced from Patagonia in South America. This dust shift occurred during a globally observed warm period, and corresponded with an interval of stronger westerly winds blowing closer to Antarctica. Our data show that decade-scale changes can be superimposed on longer intervals of intensified wind strength.