Abstract
Abstract. A chironomid-based calibration training set comprised of 100 lakes from south-western China was established. Multivariate ordination analyses were used to investigate the relationship between the distribution and abundance of chironomid species and 18 environmental variables from these lakes. Canonical correspondence analyses (CCAs) and partial CCAs showed that mean July temperature is one of the independent and significant variables explaining the second-largest amount of variance after potassium ions (K+) in 100 south-western Chinese lakes. Quantitative transfer functions were created using the chironomid assemblages for this calibration data set. The second component of the weighted-average partial least squares (WA-PLS) model produced a coefficient of determination (r2bootstrap) of 0.63, maximum bias (bootstrap) of 5.16 and root-mean-square error of prediction (RMSEP) of 2.31 °C. We applied the transfer functions to a 150-year chironomid record from Tiancai Lake (26°38′3.8 N, 99°43′ E; 3898 m a.s.l.), Yunnan, China, to obtain mean July temperature inferences. We validated these results by applying several reconstruction diagnostics and comparing them to a 50-year instrumental record from the nearest weather station (26°51′29.22′′ N, 100°14′2.34′′ E; 2390 m a.s.l.). The transfer function performs well in this comparison. We argue that this 100-lake large training set is suitable for reconstruction work despite the low explanatory power of mean July temperature because it contains a complete range of modern temperature and environmental data for the chironomid taxa observed and is therefore robust.
Highlights
South-western China is an important region for examining changes in low- and mid-latitude atmospheric circulation in the Northern Hemisphere. It lies at the intersection of the influence of the northern hemispheric westerlies and two tropical monsoon systems, namely the Indian Ocean south-west monsoon (IOSM) and the East Asian monsoon (EAM), and should be able to inform us about changes in both the latitude and longitude of the influence of these respective systems through time
Climate parameters including mean July temperatures and mean annual precipitation used in this study are interpolated from climate surfaces derived from a mathematical climate surface model based on the limited meteorological data and a digital terrain model (DTM) applied to the whole of the wider Tibetan region (400 × 3000 km) (Böhner, 2006)
We argue that developing a mean July air temperature (MJT) transfer function is appropriate for this large lake training set because MJT is independent of other variables (e.g. Rees et al, 2008; Chang et al, 2015a)
Summary
South-western China is an important region for examining changes in low- and mid-latitude atmospheric circulation in the Northern Hemisphere. It lies at the intersection of the influence of the northern hemispheric westerlies and two tropical monsoon systems, namely the Indian Ocean south-west monsoon (IOSM) and the East Asian monsoon (EAM), and should be able to inform us about changes in both the latitude and longitude of the influence of these respective systems through time. Reconstructing changes in circulation requires information about several climatic parameters, including past precipitation and temperature. While there are reasonable records of precipitation from this region In order to understand the extent and intensity of penetration of monsoonal air masses, robust summer temperature estimates are vital as this is the season that the monsoon penetrates south-western China.
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