Chironomid record from the Little Ice Age in Laguna Azul, Southern Patagonia (Argentina)

MARTÍN, R.S.,; MASSAFERRO, J.; RAMÓN MERCAU. J.; LÜCKE, A.; MAYR, C.,; LAPRIDA, C.

Mendoza

Congreso; 4th International Paleontological Congress; 2014

IPA

Due to its unique geography and climate, paleoenvironmental records from the Patagonian region are key to understanding the climatic variability of the last millennia. Lacustrine sediments are among the few records of past environmental conditions in the Patagonian Steppe and allow the study of a wide variety of inorganic and organic proxies. Chief among them are chironomids (Insecta: Diptera), which show great potential for reconstructing mean air temperature. Here we present the chironomid record of a radiocarbon-dated sediment core AZU03/4-1 obtained from the steppe crater lake Azul (52°05? S, 63°35?W) for the period between ~ 1550 ? 1840 AD, which comprises the approximate time window of the so-called Little Ice Age. A zonation was performed on the profile by means of the Optimal Sum-of-Squares method and its significance was statistically validated by comparing against a Broken-Stick null model, which yielded four statistically significant divitions. Zone A (~1550 ? 1645 AD) is characterized by the dominance of Tanytarsini species with Parachironomus among the accompanying taxa, which indicates relatively cold conditions. Upcore, the latter species dwindles and the former increase their abundance, which defines Zone B (~1645 - 1740 AD), corresponding to a colder period. Between 1740 ? 1800 AD Tanytarsini 1A disappears, and the accompanying Parachironomus increases its relative abundance again, pointing to a slight amelioration of temperature and a lowering in the lake level related to warmer conditions; fluctuations in the remaining Tanytarsini species define the remaining divisions in the profile indicating anew a very cold pulse starting around 1830. These results are in accordance with the conclusions of a multi-proxy study performed on the same sediments, which postulates climatic-driven lake level fluctuations for the analyzed time window with a relative temperature minimum between ~ 1670 ? 1890 AD, attesting to the suitability of chironomids for paleoenvironmental reconstruction in Patagonia.