AMS radiocarbon dating and varve chronology of Lake Soppensee: 6000 to 12000 14C years BP

Abstract

For the extension of the radiocarbon calibration curve beyond 10000 14C y BP, laminated sediment from Lake Soppensee (central Switzerland) was dated. The radiocarbon time scale was obtained using accelarator mass spectrometry (AMS) dating of terrestrial macrofossils selected from the Soppensee sediment. Because of an unlaminated sediment section during the Younger Dryas (10000-11000 ~4C y BP), the absolute time scale, based on counting annual layers (varves), had to be corrected for missing varves. The Soppensee radiocarbon-varve chronology covers the time period from 6000 to 12 000 14C y BP on the radiocarbon time scale and 7000 to 13000 calendar y BP on the absolute time scale. The good agreement with the tree ring curve in the interval from 7000 to 11450 cal y BP (cal y indicates calendar year) proves the annual character of the laminations. The ash layer of the Vasset/Killian Tephra (Massif Central, France) is dated at 8230_+ 140 14C y BP and 9407_+44 cal y BP. The boundaries of the Younger Dryas biozone are placed at 10986_+69 cal y BP (Younger Dryas/Preboreal) and 12125_+ 86 cal y BP (Aller6d/Younger Dryas) on the absolute time scale. The absolute age of the Laacher See Tephra layer, dated with the radiocarbon method at 10 800 to 11200 ~4C y BP, is estimated at 12 350 _+ 135 cal y BP. The oldest radiocarbon age of 14190_+120 14C y BP was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile. For the late Glacial, the offset between the radiocarbon (10000-12000 14C y BP) and the absolute time scale (11400-13000 cal y BP) in the Soppensee chronology is not greater than 1000 years, which differs from the trend of the U/Th-radiocarbon curve derived from corals.

Deposition models for chronological records

“…The first example to be considered is a the varved lake sediment from Soppensee (Hajdas et al (1993) and Hajdas et al (2000)). This is an interesting example because it shows that the approaches outlined here can be applied both in terms of depth and in terms of varve count.…”

“…The example of Soppensee (Hajdas et al, 1993) is chosen here because it has a number of interesting features:…”

“…In the end, in addition to the outliers already identified by Hajdas et al (1993), further data-points were rejected on the basis that they gave low agreement with the selected models (Blockley et al, 2006b). …”

“…Because this study was drawing on already published material it was thought most appropriate to use the different sedimentary units (I to VI) of the deposit defined by Hajdas et al (1993).…”

14C Dating of Terrestrial Moss in Tern Lake Deposits, Antarctica

“…It gives more precise ages than can be obtained on bulk sediment. Therefore, this method has become quite common in lake studies (Lotter 1991;Hajdas 1993). Fildes Peninsula is a major colony of terrestrial moss in Antarctica, but moss fragments and authigenic carbonates occur only in very small amounts.…”