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Beryllium-10; Varved lake sediment
DDC:
550 - Earth sciences
Abstract:
As part of understanding and reconstructing our climate history it is important to investigate the link between climate and solar activity. Ice cores and ocean sediments have provided information on a range of timescales on atmospheric 10Be production, which is a proxy for past solar activity due to its cosmogenic nature of production. We here present results from the first, to our knowledge, multi-centennial and annual resolution study of 10Be in varved lake sediments. Varves were sampled over an interval covering the period 1468–2006 CE in sediment cored from Lake Lehmilampi in eastern Finland. The measured concentrations were converted into annual 10Be deposition rates by using the weights of dried samples as an estimation of sedimentation rates and scaling the result from sampling to catchment area size. We compare the lake catchment 10Be deposition rates to those derived from the Greenlandic ice cores NGRIP and Dye-3 along with past solar activity. Sediment 10Be concentrations range 2.1–17.6 × 108 atoms g−1. The high end of this range is represented by a limited number of samples, and the average is near the lower end at 4.1 × 108 atoms g−1. The deposition rates range 0.5–3.9 × 106 atoms cm−2 year−1, with an average of 1.8 × 106 atoms cm−2 year−1 (0.057 atoms cm−2 s−1). We note higher 10Be deposition during the Spörer (∼1415–1535 CE) and Maunder (∼1645–1715 CE) solar minima, and also at the onset of the Dalton (∼1790–1830 CE) minimum. Equally high 10Be values in the 1840s and lower deposition during the Dalton minimum are not consistent with contemporaneous solar activity. Although this may in part be a result of incomplete measurements in the 19th century, it also shows the complexity of deposition and the intricacy of reconstructing past solar activity from sediment 10Be data. A comparison with ice core data reveals particularly good agreement between sediment and Dye-3 10Be flux around 1500–1750 CE.
