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

MUSOTTO, L.; FERNANDEZ, M.; BORROMEI, A. M.; A., PONCE, J. F.; CORONATO, A.; RYDBERG, J.

Congreso; IAL IPA 2022; 2022

Laguna Amalia (53°35´09.4´´S; 68°26´34.3´´W) is one of the most prominent semi-permanentwater bodies in the northern Tierra del Fuego. It is an ephemeral, shallow lake locatedin the semiarid steppe. We studied a 103 cm long sedimentary core to reconstruct theenvironmental conditions during the last ca. 7100 cal yr BP. The mutiproxy analyses (pollen/spores, fungal remains, freshwater algae, grain size, and sediment composition) togetherwith the geomorphological features of the landscape allowed us to interpret changes in thelake level. The sediments are dominated by medium to fine silt, with variable percentages ofclay, fine and very fine sand. Between 78 and 8 cm depth, there are abundant sandy-silt andsilty-sand laminae that could be related to eolian activity around the lake. Organic mattercontent increased from about 6000 cal yr BP, while carbonate content displayed a decreasingtendency. The pollen assemblages throughout the entire profile revealed a landscapedominated 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 ofsedges (Cyperaceae), and hygrophilous taxa (Iridaceae, Juncaginaceae, Myriophyllum).The Andean forest communities were represented by the record of long-distance Nothofaguspollen. In general, wet periods were characterized by retraction of halophytes, proliferationof Pediastrum, presence of Diploneis spp., and massive silty sediments. Conversely, the dryintervals showed the spread of halophytic vegetation around the lake, increased amounts ofBotryococcus and Spirogyra, and records of Surirella tuberosa. Diatom assemblages weredominated by Diploneis elliptica, Diploneis sp. and S. tuberosa, although valve counts weregenerally low. These environmental changes would be related to variations in the strengthand/or latitudinal position of westerly winds during the middle to late Holocene