350 years of Chironomidae assemblages in a Southern patagonian lake, Argentina: trends and sensitivity. VI International Limnogeological Congress

MARTIN R.; MASSAFERRO, J.; MAYR, C.; AGUIRRE-URRETA, B., PAZOS, P.J., RAMOS, V.A., OTTONE, E.G., LAPRIDA, C. Y LAZO, D.G.

Reno

Congreso; VI International Limnogeological Congress; 2015

The Little Ice Age (LIA) usually refers to climatic anomalies over the northernhemisphere between the 13th and mid-19th century. For the mid-high-latitudesof South America, documentary evidence of this climaticevent is not available due to the sparse settlement of thecontinental regions during this period.Additionally, the number of proxy-basedreconstructions is still fragmentary. As such, tempo and mode of the LIA is still a matter of debate, especially in Southern Patagonian steppe. For example, the temporal range of the LIA, based on glacial maximum extent in the Southern Andes is generally agreed to have lasted between ~AD 1600and ~AD 1900, but high-resolution temperature/precipitation reconstructions are still extremely scarce. Our study focuses on the recent history of Laguna Azul (52°05?S, 69°35?W), a small closed-basin lake located in the southern Patagonian steppe. As chironomids are sensitive indicators of temperature conditions, we set out to address whether the LIA climate cooling,as indicated by glacial Patagonian maximum extent,altered the ecological status of this lake using fossil and subfossil Chironomidae communities from the sediment cores AZU03/5, AZU03/4-1 and AZU03/4-2.The lake was chosen for study because it is a remote lake located in the belt of the South Hemisphere Westerly Winds and is therefore theoretically closelycoupled with atmospheric forcing factors. A furthermotivation for selecting this particular lake wasthat previous paleolimnologicalinvestigation (Mayr et al. 2005) suggested there had been long-term interactions between regional climate and lake status.These authors defined two lake status: between AD 1400 and AD 1700, period characterized by a decreasein lake level, and between AD 1700 and AD 1900, period characterized by rising lake level. Chironomid assemblages were analyzed since AD 1450 until the late twentieth century.Surprisingly, communities did not exhibit speciesturnover during the last 350 years, being the Tanytarsini the dominant taxa throughout this period (Figure 1). This genus includes species generally associated with cold and/or oxygenatedwaters, specially the cold stenotypic Tanytarsini sp. 2-type. The stability of the cold-associated chironomid communities suggests cold conditions similar to modern onesduring the temporal range of the LIA.However, asmall directional communityshift was detected between AD 1650 and AD 1750. This shift suggests a slightly cooler period, which partially coincides with theMaunder Solar Minimum.