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- Fontana, Sonia L.
(författare)
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Radiocarbon chronologies of Holocene lacustrine sediments from the southern coast of Buenos Aires Province, Argentina
- 2007
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Ingår i: Radiocarbon. - 0033-8222 .- 1945-5755. ; 49:1, s. 103-116
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Tidskriftsartikel (refereegranskat)abstract
- Two lacustrine sediment sequences, La Olla 1 and Laguna del Sauce Grande, on the southern coast of Buenos Aires Province, Argentina, were investigated for carbon reservoir effects, which may influence age-depth chronologies. Fruits of the submerged macrophyte Ruppia cf. maritima from the La Olla 1 sequence, and gastropod shells of Heleobia parchappii from the Laguna del Sauce Grande core, were radiocarbon dated. In addition, terrestrial plant remains and shells of living specimens were dated to assess the presence and magnitude of a reservoir effect. A reservoir age of about 800 14C yr is estimated for the aquatic plant samples of La Olla 1 for the early Holocene. The reservoir effect is attributed to the inwash of 14C-deficient bicarbonate from the surrounding sand dunes. The decay of marine organisms and salt spray are likely the main sources of 14C-deficient carbon. The magnitude of the reservoir effect is consistent with marine reservoir offsets reported for the region. The 14C measurements on shells of living and fossil specimens of Heleobia parchappii indicate the absence of a reservoir effect at Laguna del Sauce Grande, which may be due to the large size and shallow nature of the lake. This study shows how the reservoir ages of 2 close-by lakes in very similar geological settings can be largely different. These results have significant implications for the interpretation of 14C dates from lacustrine deposits in the region.
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- Gisecke, Thomas, et al.
(författare)
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Revisiting pollen accumulation rates from Swedish lake sediments
- 2008
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 18:2, s. 293-305
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Tidskriftsartikel (refereegranskat)abstract
- Early hope that the estimation of pollen accumulation-rates (PAR) from lake sediments would permit the quantitative reconstruction of past vegetational composition abated when results from several experiments uncovered the problems of the method. A review of monitoring experiments, mainly conducted between 1960 and 1980, shows that basin size, transport of pollen with flowing water and sediment redeposition and focusing are the most important factors influencing pollen deposition in lakes. With careful site selection most of these factors can be rendered unimportant or constant. It is shown that PAR estimates from three small lakes in a rather homogeneous forest region are very similar for the last 9000 years. Results from monitoring of pollen deposition in pollen traps provides important information in the interpretation of PAR. Monitoring experiments were conducted to explore the deposition of pollen on and in small lakes. Pollen deposition in pollen traps floating on small lakes was not different from pollen deposition observed on land. PAR estimates from lake sediments were comparable with the results of pollen monitoring obtained with Tauber-type traps. A proportion of airborne pollen deposited on a lake surface is lost during the transport to the lake sediment. The amount of pollen that is lost differs between pollen types.
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