The leading mode of Indian Summer Monsoon precipitation variability during the last millennium

Abstract

The “internally” generated intraseasonal variability of the Indian Summer Monsoon is characterized by intermittent periods of enhanced (“active”) and deficient (“break”) precipitation, which produce a quasi east‐west precipitation dipole over the Indian subcontinent. Here we present multicentennial‐length and near annually‐resolved reconstructions of monsoon precipitation, inferred from absolute‐dated and instrumentally calibrated speleothem oxygen isotope records from regions (central and northeast India) that have diametric responses to active‐break monsoon circulation patterns. On centennial timescales (AD 1400–2008), precipitation variability from these two regions exhibit opposing behavior, oscillating between periods with a persistently “active‐dominated” (AD ∼1700 to 2007) and a “break‐dominated” (AD 1400 to ∼1700) regime. The switch between these regimes occurs abruptly (within decades) at a time (AD ∼ 1650–1700) when a proxy record of upwelling intensity from the Arabian Sea suggest an abrupt increase in the monsoon winds. On the basis of these observations, we hypothesize that the frequency distribution of active‐break periods varies on centennial timescales, implying a leading role of internal dynamics in governing the ISM response to slowly‐evolving changes in the external boundary conditions.

Hydroclimatic shifts in northeast Thailand during the last two millennia – the record of Lake Pa Kho

“…This coincides, within error margins, with the start of a weaker summer monsoon phase recorded in Wanxiang Cave (Zhang et al, 2008) (Figure 4a), and also compares to the intervals of lower precipitation (AD 1249-1325; 1390-1420) inferred from speleothem δ 18 O values in Dayu Cave (Tan et al, 2009) (Berkelhammer et al, 2010;Sinha et al, 2011aSinha et al, , 2011bSinha et al, , 2007; (c) δ 13 C org data from Lake Pa Kho (this study); (d) grain size variations in sediment core DY6-MGS of Cattle Pond, Dongdao Island (Yan et al, 2011); (e) Palmer Drought Severity Index (PDSI) derived from the Monsoon Asia Drought Atlas (MADA) for the region between 10 and 20°N and 95-115°E (Buckley et al, 2007(Buckley et al, , 2014Cook et al, 2010;D'Arrigo et al, 2011;Sano et al, 2009); (f) δD wax from marine cores 31 MC and 34 GGC from southwest Sulawesi (Tierney et al, 2010). The vertical light gray bars represent higher effective moisture/a strengthened summer monsoon, and the dark gray bars represent lower effective moisture/a weakened summer monsoon.…”

“…The offset of 60-140 years between the two data sets at the beginning and end of the weaker summer monsoon period, respectively, may stem from chronological uncertainties. Upwelling indicators (Globigerina bulloides) in sediments from the northwestern Arabian Sea also show a weakening of the summer monsoon starting around AD 450 (Anderson et al, 2010(Anderson et al, , 2002, and the composite speleothem δ 18 O records from Indian caves give evidence for decadal intervals of a distinctly weaker summer monsoon between AD 650-900 (Berkelhammer et al, 2010;Sinha et al, 2011aSinha et al, , 2007 (Figure 4b). These time intervals of a stronger/weaker Asian summer monsoon, however, differ from to the δD wax record from the Makassar Strait (Figure 4 a-c and f), which suggests a weaker Asian monsoon until around AD 450 and subsequently a stronger monsoon until about AD 1000 (Tierney et al, 2010) (Figure 4f).…”

“…The terrestrial plant leaf wax (δD wax ) record established from marine sediments from the Makassar Strait, Southwest Sulawesi (Tierney et al, 2010) is the only high-resolution record extending as far back as Pa Kho, while the Wanxiang Cave δ 18 O data set commences around AD 200 (Zhang et al, 2008). All other high-resolution records only cover the last 1400 years (central India composite record) (Berkelhammer et al, 2010;Sinha et al, 2011aSinha et al, , 2011bSinha et al, , 2007; the last 1000 years (Dongdao Island) (Yan et al, 2011) or the past 700-800 years (MADA data set; Dayu Cave) (Buckley et al, 2007(Buckley et al, , 2014Cook et al, 2010;Tan et al, 2009) (Figure 4a-f).…”

“…These time intervals of a stronger/weaker Asian summer monsoon, however, differ from to the δD wax record from the Makassar Strait (Figure 4 a-c and f), which suggests a weaker Asian monsoon until around AD 450 and subsequently a stronger monsoon until about AD 1000 (Tierney et al, 2010) (Figure 4f). Berkelhammer et al, 2010, Sinha et al, 2011aand Sinha et al, 2007and Zhang et al (2008 infer a strengthening of the summer monsoon between AD 950-1300 from speleothem δ 18 O records (Figure 4a and b). These findings are comparable within error margins to our data set, which suggests higher effective moisture starting around AD 800 (Figure 4c), but they differ from lower precipitation inferred over Dongdao Island in the South China Sea between AD 1000-1400 (Yan et al, 2011) (Figure 4d).…”

“…Wang et al, 2005). Yet high-resolution tree ring , marine (Anderson et al, 2002;Newton et al, 2006;Oppo et al, 2009), coral (Cobb et al, 2003), speleothem (Sinha et al, 2011a;Zhang et al, 2008), and lake (Yancheva et al, 2007) studies show that substantial decadal to centennial variations in summer monsoon intensity were superimposed on the longterm trend. Various hypotheses have been brought forward through the last millennium Pages 2K, Consortium, 2013).…”