¹⁴C Chronostratigraphy for Qinghai Lake in China

Abstract

Radiocarbon accelerator mass spectrometry (AMS) techniques were used to date total organic carbon and plant seeds in the 1Fs core sequence (36°48′N, 100°08′E) from Qinghai Lake, China. This core was drilled ~18 m into Qinghai Lake sediments as part of an international cooperative research project, "Scientific Drilling at Qinghai Lake in the Northeastern Tibetan Plateau: High-Resolution Paleoenvironmental Records of Eastern Asia Linked to Global Change," which began in 2004. Based on the differences in lithology and total organic content (TOC) in core 1Fs, the core was divided into 3 sections for age-modeling purposes: the upper ~499 cm lacustrine silty clay to clay; the middle unit of silty clay with silt layers from 499-901 cm; and the lower 901-1861 cm silty clay, loess-like silt, and fine sand layers. Three different approaches are applied to the reservoir age problem. First, a simple linear regression gives an offset of 1342 yr. If the core is divided into three sections, linear regressions can be applied separately for the three segments, which results in an age estimate for the average hardwater effect of ~135 yr BP for the surface section up to 499 cm. If extrapolated for deeper sections, these results imply a higher reservoir offset for those two sections, which may be as much as 1143 and 2523 yr, but this assumes that there are no discontinuities in the core. A third approach using a wiggle-matching approach gave an offset of 196 yr. This study concludes that the reservoir age of Qinghai Lake is complex, but these new data add to our understanding of the 14 C chronology of Qinghai Lake for the last 32 ka.

Lake Qinghai sediment geochemistry linked to hydroclimate variability since the last glacial

“…Rb, Sr, and Ca/Zr stratigraphy and depositional conditions since the last glacial Zhou et al, 2014). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)…”

“…Similar to Rb and Sr behaviors, the contrasting geochemical properties of Ca and Zr cause Ca/Zr to behave in an opposite fashion to Rb/Sr: authigenic carbonate-enriched sediments have low-Rb/Sr Zhou et al (2014). The 14 C data are divided into three segments according to their respective lithology and sedimentation rates (SR).…”

“…The age model for the core 1Fs was based on accelerator mass spectrometry (AMS)-14 C dates of 52 bulk TOC, 6 Ruppia maritima seeds (from 4.16 to 4.97 m), and 7 plant remains samples (from 6.70 to 8.38 m) Zhou et al, 2014). After comparing three approaches for these 14 C dates, Zhou et al (2014) adopted the linear regressions in segments to construct the age model for the core 1Fs as shown in Fig.…”

“…After comparing three approaches for these 14 C dates, Zhou et al (2014) adopted the linear regressions in segments to construct the age model for the core 1Fs as shown in Fig. 2.…”

“…This work builds on previous work by An et al (2012) who developed an age model (cf. Zhou et al, 2014) and initial climatic reconstruction from the 1Fs. In order to identify relative contributions of eolian dust versus lacustrine precipitates to Lake Qinghai sediments under different depositional and hydroclimatic conditions, we have focused on a few geochemical tracers including Rb, Sr, and Ca/Zr for recent lake and river sediments and catchment loess, and for sediments from the core 1Fs.…”