Multi-centennial scale SST and Indian summer monsoon precipitation variability since the mid-Holocene and its nonlinear response to solar activity

Indian Summer Monsoon (ISM) shows a weak correlation with solar variability in the 20th century. However, such climatological observations on solar activity-monsoon relationship are very short and hence uncertain. A few paleomonsoon records also exhibit prominent correspondence with solar activity during early Holocene and beyond. But despite the strong recent solar minima (e.g. Maunder, Sporer, Oort, Wolf), their correlation with monsoon precipitation is weak and inconclusive. Additionally, many of the earlier studies have been from the western Arabian Sea that provides records of the ISM wind intensity instead of the ISM precipitation. We present here mid-Holocene to recent sea surface temperature (SST) reconstructed from Mg/Ca measurements of planktic foraminifera (Globigerinoides ruber; white, sensu stricto) on a centennial-scale resolution from the southeastern Arabian. These measurements are used to correct the oxygen isotope ratios of G. ruber to reconstruct salinity related to monsoon runoff in this region more precisely than hitherto. The long-term trend indicates that the ISM precipitation has declined since the mid-Holocene similar to the solar activity. On shorter multi-centennial timescale, we show that the ISM precipitation declined concurrently with the recent periods of strong solar minima, but lagged by a couple of hundred years beyond 1300 yr BP toward the mid-Holocene - confirmed statistically using wavelet analysis. This nonstationary phase relationship between the ISM and the solar activity indicates the possible influence of the tropical coupled ocean-atmosphere phenomenon.