Tropical South American Climate Variability During Late MIS 3: Low‐Latitude Controls and High‐Latitude Influences in the Community Earth System Model Version 2 (CESM2)

Abstract Paleoclimate evidence suggests that high‐latitude ocean‐atmosphere processes impact tropical South American temperature and precipitation dynamics during glacial cycles. Although variability in the North Atlantic has been implicated in tropical climate shifts during the latest Pleistocene, the links between high‐ and low‐latitude ocean–atmosphere dynamics during late Marine Isotope Stage 3 (MIS 3) remain poorly resolved. Here, we use the Community Earth System Model (CESM2) to investigate how evolving boundary conditions, combined with meltwater events in the North Atlantic, may have affected South American climate at 30 ka BP, near the timing of Heinrich Event 3. Simulations without increased meltwater flux produce near‐surface tropical cooling of ∼1.7°C and mid‐tropospheric (524 hPa) cooling of ∼2.4°C relative to pre‐industrial (PI) conditions, yielding temperatures ∼0.2–0.4°C warmer than those simulated for the Last Glacial Maximum. Increasing meltwater flux across regions of the North Atlantic perturbs Atlantic Meridional Overturning Circulation, and leads to tropical near‐surface cooling (relative to PI) of ∼1.9–2.4°C and cooling of 2.5–3.2°C near the alpine glacial limit. In addition, most meltwater experiments produce an intensified Intertropical Convergence Zone and a strengthened South American Summer Monsoon. While orbital forcing emerges as the dominant driver of latest Pleistocene tropical climate conditions, our results suggest that high‐latitude processes can amplify low‐latitude temperature and hydroclimate responses during meltwater events. As such, some tropical glaciers at ∼30 ka BP were likely more extensive than during the LGM due to enhanced precipitation and modest alpine temperature changes.