Middle to Late Holocene environmental changes in the fuegian steppe (northern Tierra del Fuego, Argentina) based on multiproxy analyses from Laguna Amalia

MUSOTTO, LORENA LAURA; FERNÁNDEZ, MARILEN; BORROMEI, ANA MARÍA; PONCE, J. FEDERICO ; CORONATO, ANDREA; RYDBERG, JOHAN

Bariloche

Congreso; IAL-IPA 2022 meeting, Lagos memorias del Territorio Lakes memories of the Landscape; 2022

Varias Instituciones

Laguna Amalia (53°35´09.4´´S; 68°26´34.3´´W) is one of the most prominent semi-permanent water bodies in the northern Tierra del Fuego. It is an ephemeral, shallow lake located in the semiarid steppe. We studied a 103 cm long sedimentary core to reconstruct the environmental conditions during the last ca. 7100 cal yr BP. The mutiproxy analyses (pollen/spores, fungal remains, freshwater algae, grain size, and sediment composition) together with the geomorphological features of the landscape allowed us to interpret changes in the lake level. The sediments are dominated by medium to fine silt, with variable percentages of clay, fine and very fine sand. Between 78 and 8 cm depth, there are abundant sandy-silt and silty-sand laminae that could be related to eolian activity around the lake. Organic matter content increased from about 6000 cal yr BP, while carbonate content displayed a decreasing tendency. The pollen assemblages throughout the entire profile revealed a landscape dominated by grasslands (Poaceae) along with open shrub vegetation of Asteraceae subf. Asteroideae, dwarf shrubs of Empetrum rubrum and forbs (Caryophyllaceae, Acaena, Gunnera, Euphorbiaceae, Valeriana, Caltha). The halophyte communities (Chenopodiaceae) developed in the surroundings of this shallow lake accompanied by low proportions of sedges (Cyperaceae), and hygrophilous taxa (Iridaceae, Juncaginaceae, Myriophyllum). The Andean forest communities were represented by the record of long-distance Nothofagus pollen. In general, wet periods were characterized by retraction of halophytes, proliferation of Pediastrum, presence of Diploneis spp., and massive silty sediments. Conversely, the dry intervals showed the spread of halophytic vegetation around the lake, increased amounts of Botryococcus and Spirogyra, and records of Surirella tuberosa. Diatom assemblages were dominated by Diploneis elliptica, Diploneis sp. and S. tuberosa, although valve counts were generally low. These environmental changes would be related to variations in the strength and/or latitudinal position of westerly winds during the middle to late Holocene.