Last millennial environmental reconstruction based on a multi-proxy record from Laguna Nassau, Western Pampas, Argentina

We present a multi-proxy record from Laguna Nassau (LN), a shallow lake which developed in a blowout depression in the semi-arid sandy lowlands of the Western Pampas of Argentina. This multi-proxy stacked record reveals the evolution of an incipient water body subjected to warm and dry conditions from ~900 to 770 cal yr BP, an interval that is coeval with the Medieval Climatic Anomaly (MCA) period. Vegetation was dominated locally by Typha, and regionally by the Espinal, represented by Celtis, along with psammophytic-halophytic communities in sand dunes and lowlands. After that, variable water-depths and unstable conditions occurred in the water body in relation to dry and humid climatic phases until ~200 cal yr BP, likely related to a transition from warm and dry conditions, corresponding to the MCA, to a colder and wet climatic setting during a period concurrent with the Little Ice Age (LIA). This water body evolved into a shallow lake since then, with a more stable and higher water level, and regional vegetation characterized by the Espinal and psammophytic-halophytic communities mantling and stabilizing the nearby sand dunes. This evolution suggests complex hydrological responses of LN likely associated with its sensitivity to climatic variability. Our results highlight important contrasts in hydrologic balance during the MCA and LIA along the western and northeastern Pampas, suggesting important shifts mainly in the South-American Summer Monsoon at centennial timescales over the last millennium.