Variable Late Holocene 14C Reservoir Ages in Lake Bosten, Northwestern China

Kang’En Zhou,Yunping Song,Jin Zhang,Keke Yu,Dongna Yan,Jianghu Lan,Enguo Sheng,Pingqing Fu,Sheng Xu,Hai Xu

doi:10.3389/feart.2019.00328

Abstract

Radiocarbon (14C) dating has been widely used in paleoclimate reconstruction. However, the reliability of the 14C age in lake sediments is sensitive to the 14C reservoir effect, especially for a lake in arid regions. In this study, we evaluated the 14C reservoir ages under different hydroclimatic conditions over the past ~2300 years in Lake Bosten, northwestern China, by comparing with different dating results and with multi-proxy indices of a vertical-down sediment core collected in this lake. The 14C reservoir ages during ~ 1800 to 650 BP (a dry interval) are estimated to be approximately 1170 years older than those during ~ 650 -100 BP and those during 2200-1800 BP (wet intervals). We proposed that variation in 14C exchange rate between the dissolved CO2 in lake water and CO2 in the atmosphere, as well as the changing proportion of organic matter in the lake and the catchment, could have contributed to the variable 14C reservoir ages in Lake Bosten. The result of this study suggests that the 14C reservoir effect may be larger in dry periods than in wet periods in the arid/semi-arid area, which should be considered when establishing age models of lake sediment cores from these regions.

Highlights

Radiocarbon (14C) dating has been widely used to establish geochronology less than ∼50,000 years (Hughen et al, 2004; Reimer et al, 2009), using a variety of dating materials, including fossils of terrestrial and aquatic plants, bulk organic matter, etc. (Snyder et al, 1994; Bennike, 2000)
Sedimentation rate based on this 1964-year time marker is ∼0.29 cm/year. 137Cs activity increases rapidly from zero at 22 cm, indicating the beginning of atmospheric 137Cs fallout, corresponding to the 1952 AD time marker (Yu et al, 2017; Yan et al, 2019)
Some aquatic plants in the lake use CO2 in atmosphere and dissolved inorganic carbon (DIC) in water for photosynthesis, which will result in parts of the “old carbon” used in photosynthesis (Olsson, 2009). (3) the pH value, salinity, and nutrient concentration of lake water may affect the primary productivity of lake, the 14C exchange rate, and the old carbon reservoir age (Fontes et al, 1996; Shen et al, 2005)

Summary

Introduction

Radiocarbon (14C) dating has been widely used to establish geochronology less than ∼50,000 years (Hughen et al, 2004; Reimer et al, 2009), using a variety of dating materials, including fossils of terrestrial and aquatic plants, bulk organic matter, etc. (Snyder et al, 1994; Bennike, 2000). In many cases, due to the paucity of sufficient terrestrial plant debris in lake sediments, bulk organic matter and aquatic shells are frequently used in radiocarbon dating, and the 14C ages of these materials are generally more or less contaminated by the 14C reservoir effect. This is due to the disequilibrium of 14C concentration between aquatic CO2 and atmospheric CO2, and due. The lowest salinity of the lake is in the Kaidu River estuary (0.20–0.28%; Mischke and Wünnemann, 2006), and the maximum value is in the eastern part of the lake (>2.5%; Jiu et al, 1990). The pH value of lake water is 8.3–9.0 (Mischke and Wünnemann, 2006)

Results

Discussion

Conclusion