The Pampean region (Argentina) underwent larger variation in aridity than in temperature during the late Pleistocene: New evidence from the isotopic analysis of mammalian taxa

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During the Pleistocene intense climatic changes occurred corresponding with the alternation of interglacial and glacial periods. By means of stable isotope analysis on fossil mammals, this research allows the assessment of the palaeoecological and palaeoclimatic conditions, including the possible scenarios for the atmospheric circulation pattern during three key phases of the late Pleistocene in the Pampean region of Argentina: Last Interglacial (LIG, MIS 5e; unpublished data), Last Glacial Maximum (LGM; 28,170–19,849 cal BP yrs), and post-Last Glacial Maximum (post-LGM, 17,281–11,500 cal BP yrs). Tooth enamel δ13C values of mammals from the Last Glacial Maximum showed an increase in C4 plants consumption compared to the other two phases studied, which may be related to a reduction in forest cover due to a combination of environmental factors such as decreased pCO2atm and increased aridity. We evaluated mean annual precipitation (MAP) and mean annual temperature (MAT) variability from tooth enamel δ13C and δ18O values, which showed a greater variation in precipitation between phases than in temperature. This result enabled us to propose two climate regimes for the studied temporal sequence, an arid-temperate regime, and a humid-temperate regime, which were mostly regulated by variations in atmospheric circulation.