ABSTRACT
The East Asian summer monsoon (EASM) exhibits considerable decadal variations since the late 20th century. Efforts to examine long-term behaviors and dynamics of the EASM are impeded largely due to the shortness of instrumental meteorological records. So far, reconstructions of the EASM with annual resolution from its core regions remain limited. We conduct the first 200-year robust EASM reconstruction based on tree-ring cellulose δ18O records derived from Pinus massoniana trees growing in the middle Yangtze River basin, one of the core EASM areas. The δ18O chronology accounts for 46.2% of the actual variation in an index of the EASM from 1948 to 2014. The reconstructed EASM indicates that the monsoon intensity was below average before the 1950s, peaked in the 1950s-1970s, and then began to decline. The reconstructed EASM is negatively correlated with the El Niño-Southern Oscillation (ENSO), but this teleconnection is dynamic through time, i.e. enhanced (reduced) ENSO variability coheres with strong (weak) EASM-ENSO connections. In addition, despite high ENSO variability since the 1980s, the EASM-ENSO relationship weakened possibly due to anthropogenic impact, particularly aerosol emissions.
Subject(s)
Cyclonic Storms/history , Oxygen Isotopes/analysis , Pinus/metabolism , China , Asia, Eastern , History, 20th Century , History, 21st Century , Rain , Rivers , Seasons , Trees , WeatherABSTRACT
To explore the effects of Spartina alterniflora invasion in a seaward direction on variations of inorganic sulfur forms in marsh soils, the levels of inorganic sulfur forms (H2O-S, Adsorbed-S, HCl-Soluble-S and HCl-Volatile-S) were determined in bare flat (BF, before invasion), S. alterniflora marsh after seaward invasion for one year (SA') and S. alterniflora marsh after seaward invasion for three years (SA) in Shanyutan of the Minjiang River estuary with the method of space-for-time substitution. Results showed that the seaward invasion of S. alterniflora altered the stocks and distribution of inorganic sulfur form in marsh soils. Compared with BF, the contents of H2O-S, Adsorbed-S and HCl-Volatile-S in soils of SA increased by 52.6%, 78.2% and 21.0%, respectively, while that of HCl-Soluble-S decreased by 3.4%. In contrast, the levels of H2O-S, Adsorbed-S and HCl-Soluble-S in soils of SA' increased by 43.9%, 70.6% and 29.6%, respectively, whereas that of HCl-Volatile-S decreased by 11.6%. The contents of total inorganic sulfur (TIS) in soils of SA and SA' increased by 40.7% and 37.8%, while the stocks of TIS increased by 26.8% and 31.4%, respectively. The key factors affecting different forms of inorganic sulfur in marsh soils had changed due to the seaward invasion of S. alterniflora. In particular, the key factors affecting the variations of H2O-S contents changed from soil grain composition and bulk density in BF to soil organic matter in SA' and SA. The seaward invasion of S. alterniflora significantly increased the content of TIS in marsh soils, which was mainly contributed by H2O-S and Adsorbed-S. Thus, it was concluded that the seaward invasion of S. alterniflora significantly increased the supply capacity of available sulfur in marsh soils, which, to some extent, accelerated its seaward invasion.
