Evolution of subantarctic ecosystems during the last ∼2800 years in Lago Mitta (∼55°S), Isla Navarino, Fuegian archipelago

Abstract

As the only landmass that extends continuously from 52°S to 56°S, the Tierra del Fuego archipelago (TDF) provides a unique opportunity to track the Southern Westerly Winds (SWW) at subantarctic latitudes. Currently, the lack of consensus on centennial-scale SWW evolution during the late Holocene introduces uncertainty in understanding the full range of SWW variability. Here we present bidecadally resolved pollen, macroscopic charcoal, and diatom records spanning the last ∼2800 years from Lago Mitta, a small closed-basin lake located south of the Beagle Channel (55°S). Our aim is to examine terrestrial and aquatic ecosystem dynamics at this site and relate them to SWW variability in TDF. Closed-canopy forests dominated throughout the record, with modest canopy openings between ∼2.5–2.3, ∼2–1.8, ∼1.5–1.3, ∼0.8–0.7, and <0.1 cal ka BP, generally coinciding with local fire episodes. The highly dynamic diatom record transitions from benthic- to planktic-dominated assemblages, marked by abrupt transitions among planktic species (i.e., Aulacoseira ambigua, Discostella pseudostelligera, Asterionella formosa). Increasingly wet and cool conditions drove a millennial-scale lake-level rise, overprinted by centennial-scale shifts in forest structure, local fires, and water-column reorganization. The past millennium was characterized by a rise in Asterionella formosa, a diatom indicator of moderate nutrient enrichment, reflecting enhanced runoff. We infer relatively weak SWW influence between ∼2.8 and 1.6 cal ka BP, followed by an intensification culminating between ∼0.6 and 0.1 cal ka BP. Lago Mitta provides a detailed perspective on SWW variability, consistent with other TDF records that show similar but less temporally resolved trends.