Silvina Stutz
MS Tonello, D Navarro, CM Borel, SL Fontana, F García-Rodriguez, MA Gonzalez Sagrario and MC Rayó, Instituto de Investigaciones Marinas y Costeras CONICET, Univ. Nacional de Mar del Plata, Argentina [silstutz@gmail.com]
Climate variability during the last 1500 years at pampa plain (southern South America) based on multiproxy analysis
Palaeoenvironmental information based on biological proxies (pollen, non-pollen palinomorphs, plant macro remains and associated fauna) from three shallow lakes located at southeast Pampa plain (37°-38°S; 57°-58°W) is used to infer climatic conditions during the last 1500 cal yr BP. The present lakes exhibit frequent fluctuations in their water level and extension, leaving flooded or uncovered surrounding areas, depending on precipitation. Similar and synchronic patterns allow us to recognize four phases in the evolution of the lakes. Between 1500 and ca. 700 cal yr BP, the surrounding plant community is usually dominated by Chenopodiaceae or co-dominated by Chenopodiaceae-Cyperaceae. Charophytes (Chara spp., Tolypella sp., Nitella sp.) dominate the water body, indicating a clear-lake state. After 700-500 cal yr BP these clear and shallow lakes change gradually towards turbid conditions, with time-lags due to intrinsic characteristics of each lake. There is a transition from Chenopodiaceae- to Cyperaceae-dominated vegetation. Charophytes noticeably decrease while Myriophyllum sp., Potamogeton sp., Zannicchellia sp. and free-floating macrophytes increase. Also, planktonic clorophytes (Pediastrum sp., Scenedesmus sp., Tetraedrom sp.) begin to increase their values. Between ca. 300 and 100 yr cal BP Cyperaceae dominates the surrounding plant communities accompanied by Azolla filiculoides, Lemnaceae, Ricciocarpus natans and submerged macrophytes like Myriophyllum sp., Potamogeton sp. and Ceratophyllum sp. Planktonic chlorophytes exhibit their highest values. During this phase, turbid conditions with higher water level and/or grater extension of lake? surface are established. During the last ca. 80 cal yr BP, the biological proxies show fluctuations which could be associated to the human impact over these ecosystems. Beside changes in plant communities, climatic fluctuations are also recorded. Between 1500 and ca. 700 cal yr BP drier conditions than present are inferred. These conditions were already established at the beginning of the late Holocene. A transition phase towards more humid conditions is inferred although with some time-lags responses. Conditions more humid than present are established between ca. 300 and 100 cal yr BP. These results support the idea that in the southeast Pampa plain there is no evident signal of the Medieval Climatic Anomaly, and that the Little Ice Age is characterized by humid conditions. These climatic inferences disagree with those obtained from other authors in north and western areas of the Pampa plain. New paleolimnological reconstructions are needed to disentangle the intrinsic ecosystem variability from climate, and to elucidate if late Holocene climatic events had different expression in the Pampa plain.