Enhanced Last Glacial Aridity in the Western Pampean Plains Inferred From Southern South American Loess

Abstract

Understanding why proximal loess in southern South America (SSA) exhibits a contrasting evolution of dust deposition flux since the Last Glacial Maximum (LGM) compared to distal Southern Hemisphere (SH) archives remains an unresolved problem. To explore this, we examine dust emission, transport, and deposition in SSA over the past 43,000 years through a multiproxy analysis of a Pampean loess section. We reconstruct dust mass accumulation rates (DMAR) and their controls through quartz and feldspar luminescence dating, sediment properties, and paleoclimate simulations. Increased DMAR was observed during Marine Isotope Stage 3 (MIS3) due to greater sediment availability under more humid and windier conditions. A sharp decline from MIS3 to the LGM was linked to wetter source areas and more arid conditions in the Pampas that reduced dust emission and wet deposition efficiency, respectively, while intensified Southern Westerly Winds were outpaced by wetter proximal sources, limiting coarse dust deposition at the study site. During deglaciation, dust deposition in the Pampas occurred under windier but wetter conditions, resulting in dry sedimentation dominated by coarser fractions from nearby sources. In the Holocene, DMAR reflects the combined effects of enhanced dust emission under arid conditions in source regions and increasing precipitation after ∼3.9 ka in the Pampas. Our results provide constraints on accumulation modes and sediment provenance, showing how hydroclimate variability and sediment availability shaped SSA dust dynamics. Together, they reconcile contrasting dust flux trends between proximal Pampean loess and distal SH archives through coupled changes in source activity, depositional processes, and atmospheric circulation.