The Andean topography throughout the Cenozoic

The orogeny of the Andes is key to understanding the climatic history of South America. However, much debate remains surrounding the Andes uplift rate and horizontal extent throughout the Cenozoic era. Stable isotopes of water, primarily oxygen (δ¹⁸O_p) generated through Rayleigh distillation of precipitation, are used to estimate ancient elevations of mountain ranges. Here, we used the NCAR isotope-enabled global climate model (iCESM) to reconstruct paleoclimate conditions of various time periods across the Cenozoic, and generate water-isotope values to analyze the orogenic history of the Andes. This study presents periods from the early Eocene (~55-50 Ma), middle Miocene (~20-14 Ma), and preindustrial.

We find that variability in modeled δ¹⁸O_p over the Andes is primarily dependent on the height of the Andes, where changes in the climatic condition are of secondary importance but are nevertheless critical for quantifying paleoaltimetry. Elevation of the Andes is most impactful due to the initialization of the South American Low-Level Jet (SA LLJ), which is only activated when the mountains are above ~2km. The SA LLJ allows distillation of δ¹⁸O_p further from the source, yielding more negative values than flat reference cases. In addition, a change from warm-to-cold climate regimes, much like the early Eocene to the middle Miocene and middle Miocene to preindustrial, further decreases δ¹⁸O_p and increases uncertainty to paleoaltimetry estimates. Our work has major implications for climate-tectonics interactions and paleoaltimetry studies.