Past climate variability during the last 1500 cal yr at pampa plain (Southern South America) based on multiproxy analysis

TONELLO, M; STUTZ, S.; NAVARRO D.; BOREL C.; GARCÍA RODRÍGUEZ, F.; GONZÁLEZ SAGRARIO M. A.; RAYÓ, C.

Medellín

Congreso; 3rd International Sumposium Climate Change and human impact in Central and South America over the last 2000 years. Observations and Models.; 2014

PAGES, UNIVERSIDAD EAFIT

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. Present lakes exhibit fluctuations in water level and extension, leaving flooded or uncovered surrounding areas, depending on precipitation. Synchronous and similar patterns allow recognize four phases in lakes evolution. Between 1500 and ca. 700 yr cal BP, surrounding plant community is dominated by Chenopodiaceae or co-dominated by Chenopodiaceae-Cyperaceae, and Charophytes (Chara spp., Tolypella sp., Nitella sp.) dominate the water body, indicating a clear state in the lakes. These clear and very shallow lakes change gradually towards turbid conditions after 700-500 cal yr BP, with time-lags due to intrinsic characteristics of each lake. There is a transition from Chenopodiaceae to Cyperaceae dominance in plant community. Charophytes noticeably decrease and Myriophyllum sp., Potamogeton sp., Zannicchellia sp. and free-floating macrophytes increase. Planktonic clorophytes (Pediastrum sp., Scenedesmus sp., Tetraedrom sp.) begin to increase their values. Between ca. 300 and 100 yr cal BP Cyperaceae dominates plant community accompanied by Azolla filiculoides, Lemnaceae, Ricciocarpus natans and submerged macrophytes: Myriophyllum sp., Potamogeton sp., Ceratophyllum sp. whereas planktonic chlorophytes exhibit their highest values. During this phase, turbid conditions with higher water level and/or extension of surface lakes are established. During the last ca. 80 yr cal BP, biological proxies show fluctuations that could be associated to the human impact over these ecosystems. Between 1500 and ca. 700 cal yr BP drier conditions than present are inferred. These conditions were already established at the beginning of 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 southeast Pampa plain there is not an evident signal of Medieval Climatic Anomaly, and that Little Ice Age is characterized by humid conditions. These climatic inferences disagree with those obtained for others authors in north and western areas of 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 Pampa plain.