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Late Holocene climate and environment of the SE Pampa grasslands, Argentina, inferred from biological indicators in shallow, freshwater Lake Nahuel Rucá
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Functional Genomics.
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2010 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, no 3, 761-775 p.Article in journal (Refereed) Published
Abstract [en]

We analyzed pollen, non-pollen palynomorphs (NPPs), calcareous microfossils, plant macrofossils, diatoms, chrysophyte cysts, opal phytoliths and organic matter content in a 123-cm sediment sequence from Nahuel Ruca Lake, a shallow, freshwater system in the southeastern Pampa grasslands, Argentina. Three stages in the lake evolution were identified. Before 3,680 cal year BP, only pollen, NPPs (dinoflagellate cysts and acritarchs) and ostracods were recovered, suggesting brackish/saline conditions in the lake and nearby areas. Freshwater conditions are, however, indicated by Myriophyllum, Pediastrum and Zygnemataceae. The brackish/saline conditions could have been caused by marine influence during a Holocene sea level high stand that affected the area ca. 6,000 year BP. Between 3,680 and 390 cal year BP, macrophyte pollen and plant macrofossils indicate increasingly freshwater conditions in the lake and the adjacent area. Diatom and ostracod assemblages, however, suggest brackish and oligotrophic conditions, giving way to freshwater and meso-eutrophic conditions toward the end of this period. The relationship between submersed macrophytes (Myriophyllum, Potamogeton, Ceratophyllum, Chara) and planktonic algae (Chlorophyta and diatoms), suggests a shift in the lake from a clear to a turbid state. This turbid state is more evident after 390 cal year BP. High values of Pediastrum, Scenedesmus and diatoms (Cyclotella meneghiniana, Aulacoseira granulata, A. muzzanensis) observed during this stage could have reduced light penetration, with consequent loss of submersed plants. Pollen and plant macrofossils in the uppermost 20 cm indicate a shallow, freshwater lake similar to present, though an increase in brackish/freshwater diatoms suggests an increase in salinity, perhaps related to periodic droughts. Opal phytoliths yield a regional paleoclimatic reconstruction that agrees closely with inferences made using pollen, mammals and sediment characteristics.

Place, publisher, year, edition, pages
2010. Vol. 44, no 3, 761-775 p.
Keyword [en]
Holocene, Multi-proxy analysis, Paleolimnology, Pampa grasslands, Shallow lake
National Category
Earth and Related Environmental Sciences Biological Sciences
URN: urn:nbn:se:uu:diva-134359DOI: 10.1007/s10933-010-9450-4ISI: 000281973500002OAI: oai:DiVA.org:uu-134359DiVA: diva2:372295
Available from: 2010-11-25 Created: 2010-11-24 Last updated: 2010-11-25Bibliographically approved

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Evolutionary Functional Genomics
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Earth and Related Environmental SciencesBiological Sciences

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