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.
Highlights
The Asian summer monsoon is the strongest monsoon system on Earth, influencing the hydroclimatic conditions of dozens of countries and livelihood of roughly half of the world’s population [1, 2]
Significant spatial correlations are found between the East Asian summer monsoon (EASM) index and summer precipitation from Climate Research Unit (CRU) TS4.03 in the middle-lower valleys of Yangtze River (Fig 1A), indicating that the tree-ring sites are located in the core regions of EASM
We provided the first EASM reconstruction from 1815 to 2014 using a P. massoniana tree-ring cellulose δ18O records in the middle Yangtze River basin, a core area of EASM
Summary
The Asian summer monsoon is the strongest monsoon system on Earth, influencing the hydroclimatic conditions of dozens of countries and livelihood of roughly half of the world’s population [1, 2]. The East Asian summer monsoon (EASM) is a subtropical monsoon encompassing East China, Japan and Korea [3, 4]. EASM reaches the northernmost location in the global monsoon system to semi-arid regions in eastern and central Asia, forming the ecotone between agricultural and animal husbandry. Abrupt shifts of EASM usually lead to anomalous hydroclimate changes in East Asia with devastating consequences for regional agriculture and socioeconomics [1, 5] and even alternation of dynasties in history [6, 7].
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