THE LAST DEGLACIATION OF PERU AND BOLIVIA

The tropical Andes of Peru and Bolivia are important for preserving geomorphic evidence of multiple glaciations, allowing for refinements of chronology to aid in understanding climate dynamics at a key location between hemispheres. Here we focus on deglaciation from Late-Pleistocene maximum positions near the global Last Glacial Maximum (LGM), synthesizing the results of the most recent published glacial geologic studies from 12 mountain ranges or regions within Peru and Bolivia where glacial moraines and drift are dated with terrestrial cosmogenic nuclides (TCN), as well as maximum and minimum limiting ages based on radiocarbon in proximal sediments. Specific valley localities show variable and heterogeneous sequences ages and extensions of paleoglaciers, but conform to a generally cogent regional sequence revealed by more continuous lake sedimentary records. The timing of the local LGM based on average TCN ages of moraine groups is 25.1 ka, but there are large uncertainties (up to 7 ka) making the relative timing with the global LGM elusive. During the Oldest Dryas, moraine boulders date to 16.1 (± 1.1) ka, suggesting that glaciers either experienced stillstands or readvances during this interval. The Antarctic Cold Reversal is another phase of stillstanding or readvancing glaciers with moraine groups dating to 13.7 (± 0.8) ka, followed by retreating ice margins through most of the Younger Dryas. The pattern of glacial variability during the Late Glacial after ~14.6 ka appears more synchronous with periods of cooling in the southern high latitudes, and out-of-phase with the overall deglacial trend in the Northern Hemisphere.