Spatial variability of the modern radiocarbon reservoir effect in the high-altitude lake Laguna del Peinado (Southern Puna Plateau, Argentina)

Abstract. The high-altitude lakes of the Altiplano-Puna Plateau in the Central Andes often have large radiocarbon reservoir effects. This combined with the general scarcity of terrestrial organic matter makes obtaining a reliable and accurate chronological model based on radiocarbon ages a challenge. As a result, age-depth models based on radiocarbon dating are often constructed by correcting for the modern reservoir effect, however, commonly without consideration of spatial variations of reservoir ages within the lake and across the basin. In order to get a better constrain on the spatial variability of the radiocarbon reservoir effects, we analyse ¹⁴C ages of modern terrestrial and aquatic plants from the El Peinado basin in the Southern Puna Plateau, which hosts the Laguna del Peinado lake fed by hydrothermal springs. The oldest ¹⁴C ages of modern samples (> 18,000 and > 26,000 BP) were found in hot springs discharging into the lake likely resulting from the input of ¹⁴C-depleted carbon from old groundwater and ¹⁴C-free magmatic CO₂. In the littoral and central part of Laguna del Peinado, modern samples ¹⁴C ages were several thousand years lower (> 13,000 and > 12,000 BP) compared to the inflowing waters as a result of CO₂ exchange with the atmosphere. Altogether, our findings reveal a spatial variability of up to 14,000 ¹⁴C years of the modern reservoir effect between the hot springs and the lake in the El Peinado basin. This study has implications for high-precision dating and accurate ¹⁴C-based chronologies in paleoclimate studies in the Altiplano-Puna Plateau and similar settings. Our results highlight the need to consider spatial and likely also temporal variations in the reservoir effects when constructing age-depth models.