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 that of distal Southern Hemisphere (SH) archives remains a major unresolved problem. To shed light on this issue, this study examines dust emission, transport, and deposition in SSA over the past 43,000 years through 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 due to greater sediment availability and humid conditions. A sharp decline during the LGM was linked to wetter source areas and arid Pampean conditions that reduced wet dust deposition efficiency, while intensified Southern Westerly Winds strengthened dust emissions from proximal sources, as well as dry coarse dust deposition at the study site. During deglaciation, dust deposition in the Pampean region occurred under windier but relatively 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 Pampean plains. 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.