Abstract
The varved sediments of Kusai Lake on the northern Tibetan Plateau are rhythmically laminated with the interaction of dark and light layers formed during winter and summer within a year. This provides opportunities to explore the seasonal fluxes of varves and, thus, assess the potential for annual-resolution climate reconstruction. Here, we define a season index (SI) based on the difference in thickness between the light and dark layers, to evaluate the factors influencing the seasonal flux of varved Kusai Lake sediments. A positive SI represents more summer flux, and a negative SI indicates more winter flux. The results showed that the summer flux was higher than the winter flux in most of the last 2280 years. The summer flux had periodicities of approximately 2.3–2.9, 27, and 99 years at the 99% confidence level and approximately 15–16, 36 and 285 years at the 95% confidence level, indicating that summer flux is affected mainly by solar activity (Gleissberg and 350 unnamed cycle) at centennial scales, by the Pacific Decadal Oscillation (Pacific Decadal Oscillation with a period of 15–25 years) at decadal scales, and by the Quasi-biennial Oscillation (Quasi-biennial Oscillation with a period of 2–3 years) at interannual scales. Noticeable increasing spikes of high winter flux corresponded well to lower solar activity and stronger Siberian high pressure (SH). The periods of high and low winter flux are generally related to the negative and positive phases of the North Atlantic Oscillation and Atlantic Multidecadal Oscillation respectively, during the last 1000 years.
Highlights
The Tibetan Plateau (TP) is widely referred to as ‘the roof of the world’
The summer flux was higher than the winter flux, as season index (SI) values have been positive in most of the years for the last 2280 years (Figure 2), indicating that the varved sediments are mainly deposited in summer
The spectral analysis results show that summer flux has periodicities of approximately 2.3–2.9, 27, and 99 years at the 99% confidence level and approximately 15–16, 36, and 285 years at the 95% confidence level
Summary
The Tibetan Plateau (TP) is widely referred to as ‘the roof of the world’. As there are numerous glaciers and the origins of major Asian rivers on the TP, it was recently acknowledged as the Asian Water Tower (Yao et al, 2015; Yao et al, 2019). Many paleoclimate records on the TP have been reconstructed based on tree rings (Kang et al, 2000; Liu et al, 2009; Zhang et al, 2014; Chen F. et al, 2016), ice cores (Yao et al, 1996; Thompson et al, 2003; Bao, 2004; Thompson et al, 2006), and varved lake sediments (Chu et al, 2011; Liu et al, 2014b; Ji et al, 2021) at the interannual and interdecadal scales, and lake sediments at centennial to glacial-interglacial scales (Liu et al, 2006; He et al, 2013b; Liu et al, 2014a; Aichner et al, 2015; Li et al, 2015; Li X. et al, 2019) These paleoclimate reconstructions are unable to discriminate seasonal climate signals and their influencing factors, as the resolution of many archives is insufficient. Spectral and wavelet analysis and regional comparisons were used to identify regular periodicities and to evaluate possible connections of summer and winter fluxes to known modes of natural variability at different timescales
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