Late Holocene stable isotopic (δ¹³C and δ¹⁵N) records of lacustrine organic matter in Guangdong Province, south China, and their palaeoenvironmental implications

Abstract

This study presents the results of TOC/TN (C/N) ratio, δ13C and δ15N analyses of lake sedimentary organic matter (OM) from the Hedong section, western Guangdong Province in south China, with the objective to reveal the history of hydrological and ecological variations in the region influenced by both the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM). Variations in δ13C and δ15N of sedimentary OM may be closely related to past climatic conditions, which results in variations in surface runoff, lake level, allochthonous and autochthonous sources of OM, and lake productivity. Based on the interpretation of these proxies, four periods, i.e. 4370–4100, 3700–2900, 2400–2100 and 1900–900 cal. a BP, are characterized by low lake level, weakened surface runoff and deteriorated status of terrestrial and aquatic ecosystems, whereas the periods 4100–3700, 2900–2400, 2100–1900 and 900–600 cal. a BP are dominated by high lake level, strengthened surface runoff, and flourishing terrestrial and aquatic plants. A remarkable positive correlation between the δ13C values of the section and the ENSO number record obtained from the tropical Pacific implies that the impact of the ISM is greater than that of the EASM in the study area. The abnormal correspondence between the δ13C and solar activity reconstructed from 10Be and 14C records in GRIP ice‐core occurred from 1500–800 and particularly from 4200–4000 cal. a BP, suggesting that these two cool and dry intervals may be caused by stronger volcanic activities that are recorded in the GISP2 and Dome C ice‐cores. This study reveals that changes in solar insolation and solar activity, as well as changes in oceanic–atmospheric circulation (e.g. the ENSO intensity) and intensive volcano eruptions may have exerted influence on late Holocene climate variability in the study area.