SENSITIVITY OF SOUTH AMERICAN PRECIPITATION TO MIOCENE CO2 VARIATIONS AND EASTERN ANTARCTIC GLACIATION

Recent work shows a strong coupling between CO₂ and temperature across the Miocene suggesting that CO₂ is the main controlling factor behind global climate variation during this time. Here, we performed a series of sensitivity experiments with the Community Earth System Model and published Miocene boundary conditions to understand the sensitivity of South American precipitation to long-term Miocene CO₂ variations and establishment of an expansive eastern Antarctic ice sheet at the mid-Miocene Glaciation (MMG). These simulations feature CO₂ variations equivalent to radiative forcings ranging from 1 to 2.5 W/m² for pre-MMG and from 0 to 1.5 W/m² for post-MMG relative to preindustrial. For both pre-MMG and post-MMG, annual mean mid-latitude (between ~30° and 40°S) precipitation scales positively with CO₂ forcing but negatively with glacial forcing. In contrast, across South American monsoon region (~10° to 20°S), annual mean precipitation shows muted dependency on CO₂ forcing, but responds strongly to MMG glaciation, epitomized in a southward shift in South Pacific Convergence Zone. Taken together, these experiments reveal a clear spatial distinction between these two precipitation regimes in response to CO₂ forcing and glaciation: mid-latitude precipitation responds positively with CO₂ forcing but negatively to eastern Antarctic glaciation. In contrast, south American monsoon region shows resistance to CO₂ forcing, but sensitivity to eastern Antarctic glaciation. Future work will engage Miocene hydroclimate records to test this model paradigm.