Boletín de la Sociedad Geológica Mexicana

Volumen 70, núm. 1, 2018, p. 173 ‒ 186

 Multiproxy response to climate- and human-driven changes in a remote lake of southern Patagonia (Laguna Las Vizcachas, Argentina) during the last 1.6 kyr

Flavia A. Quintana1,*, Nora I. Maidana2, Luciana Motta1, Julieta Massaferro1

1CENAC/APN – CONICET. Fagnano 244, 8400 Bariloche, Argentina.
2DBBE, FCEyN-UBA/CONICET. C. Universitaria, Pab. 2. Buenos Aires, Argentina.

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Laguna Las Vizcachas is a remote lake located in the southern Patagonian steppe east of the Andes, in a key area to study the effects of the climate, especially the mode and intensity of the mid-latitude westerlies which are the dominant climate drivers in this region. Pollen, diatom and chironomid records combined with sedimentological and geochemical data are used to reconstruct the environmental history of Laguna Las Vizcachas (50°42´ S; 71°59´ W; 1100 masl) from AD 400 to the present. Our results provide evidence of changing climate conditions during the last 1.6 kyr. From AD 400 to 1550, the presence of Poaceae pollen together with planktonic and small benthic diatoms suggests a gradual increase in precipitation, and persistent cold air temperatures. At ca. AD 1550, the decrease in Poaceae and the high values of small benthic diatoms are interpreted as colder temperatures, which agree with nearby records of glacial advances probably associated with the Little Ice Age. The simultaneous appearance of the cold-tolerant chironomid morpho taxa Tanytarsini supports this assumption. From AD 1750 to the present, the appearance of Ranunculaceae-type pollen, semi-terrestrial and littoral chironomids and epiphytic diatoms suggest the expansion of littoral habitats indicative of lower lake levels; which implies less precipitation than previously. Additionally, the increase of both planktonic diatoms Dicostella and Aulacoseira and the sharp decrease of small benthic diatoms is interpreted as the onset of a warming period. The appearance of Rumex and Plantagopollen is related to the arrival of Europeans and subsequent increasing human activity in the area.

Key words: pollen, chironomids, diatoms, climatic variability, last two millennia, southern Patagonia.