Weakening of the East Asian summer monsoon at 1000–1100 A.D. within the Medieval Climate Anomaly: Possible linkage to changes in the Indian Ocean‐western Pacific

Abstract

Monsoon droughts, especially on a decadal-to-centennial timescale, may have a profound impact on the populations of East Asia. Previous work has suggested that the East Asian summer monsoon (EASM) was synchronously strong across East Asia during the Medieval Climate Anomaly (MCA, 900-1300 A.D.); however, there is a dearth of studies addressing the issue of whether or not the EASM varied significantly during the entire duration of the MCA. Here we present results from a diverse range of proxy paleoclimatic records from the monsoonal and temperate Asian region in order to evaluate the occurrence of such short timescale variability within the MCA. Within the context of an overall strong EASM during the MCA, a weakening of the monsoon was detected in many of the records during the period 1000-1100 A.D. Comparison of the timing of this event with variations of sea surface temperature (SST) of the Indian Ocean-western Pacific and with proxy records of solar activity reveals a significant covariation, suggesting that the driver of the event may have resulted from changes in the Indian Ocean-western Pacific, related to changes in solar activity. To further address the issue of a terrestrial-oceanic linkage, we used the ECHAM and the global Hamburg Ocean Primitive Equation (ECHO-G) coupled climate model to simulate the variation of EASM precipitation over the last millennium. The model results suggest an interval of weak East Asian summer monsoon at 1000-1100 A.D., and they also reveal a significant positive correlation with the SST of the Indian Ocean-western Pacific.

Decadal- to centennial-scale East Asian summer monsoon variability during the Medieval Climate Anomaly reconstructed from an eastern Tibet lacustrine sequence

“…Similarities between our record and paleoclimate records from the northern EASM limit affirm the utility of the Diaolin sequence in regional hydrologic balance reconstructions ( Fig. 7; Zhang et al 2008;Tan et al 2011;Liu et al 2014;Chen et al 2015). However, regional tectonic and anthropogenic disturbance may intermittently overprint the primary climate signal (Jiang et al 2014;Xu et al 2015).…”

“…Asian paleotemperature records indicate MCA warmth and a cool LIA (Cook et al 2013;Chen et al 2015). Despite complexities inherent in moisture/precipitation proxies, observations and models suggest a stronger EASM during the MCA and weaker EASM during the LIA, with broadly similar north-south precipitation patterns to present (Liu et al 2014;Chen et al 2015). Decadalto centennial-scale effective moisture variability occurred in China at the onset of the MCA; however, well-dated paleoclimate records from climate transition zones (e.g.…”

“…Today, a stronger EASM brings heavy rainfall to northern China ([33°N) while southern China (\33°N) experiences reduced rainfall; the inverse is true during a weaker EASM (Ding et al 2008;Zhou et al 2009). This north-south geographic precipitation pattern, termed the northern flood/southern drought phenomenon (Ma and Fu 2006), has been recognized on annual to centennial timescales over the last two millennia (Ding et al 2008;Liu et al 2014;Chen et al 2015).…”

“…In recent decades, weakening of the EASM has resulted in drier conditions in northern China and wetter conditions in southern China (Ma and Fu 2006;Zhou et al 2009). Because *60 % of Earth's human population depends on EASM-derived precipitation for food production and economic stability, much research has focused on identifying and understanding mechanisms forcing inter-annual to millennial-scale variability in EASM intensity (Liu et al 2014).…”

“…Decadalto centennial-scale effective moisture variability occurred in China at the onset of the MCA; however, well-dated paleoclimate records from climate transition zones (e.g. *30°N and/or the northwestern limit of the EASM) are scarce and EASM variability is poorly understood (Tierney et al 2008;Yan et al 2011;Liu et al 2014;Chen et al 2015). Identifying the magnitude, geographic extent, and drivers of EASM variability is important because associated droughts and floods may significantly impact human cultural and economic development.…”