Multiproxy record of Holocene paleoenvironmental change, Tierra del Fuego, Argentina

We interpret Holocene environmental conditions in a subantarctic high Andean valley from palynological and diatom analysis, peat stratigraphy, and local geomorphology. The multiproxy data from Las Cotorras mire (54° 41′ 13″ S; 68° 02′ 51″ W; 420 m a.s.l.) indicate the development of a soligenous mire, as a result of a fine grained tephra layer deposition over the mineral soils sometime prior to 8000 cal yr BP. The paleoecological conditions in the mire after 8000 cal yr BP show a rapid succession from a limnic to a telmatic stage as the mire is colonized by sedges (Cyperaceae) and herbaceous communities. The upland vegetation changed from cushion and shrub heaths to an expansion of Nothofagus forest at high altitudes after 6500 cal yr BP. The peat is interbedded with clastic sediment that originates from mass wasting events or floods. These depositional changes affected the mire ecosystem water-table level and nutrient status (oligotrophic and/or eutrophic conditions). Maxima in total pollen influx at about 2800, 1100 and 700 cal yr BP coincide with heightened mineral flux, and these changes are related to precipitation and slope processes. The major vegetational change registered in the pollen record is the decline of Nothofagus pollen after 1000 cal yr BP, which reaches a minimum between ca. 680 and 300 cal yr BP. This minimum was likely caused by cool, wet conditions that coincided with the Little Ice Age (LIA) in the Southern Hemisphere. Our results indicate the sensitivity of subantarctic Nothofagus forest and mire ecosystems to changes during the Holocene.