Khare, N. and Nigam, R. 2006. Can the possibility of some linkage of monsoonal precipitation with solar variability be ignored? Indications from foraminiferal proxy records. Current Science 90: 1685-1688.
What was done
The authors examined variations in angular-asymmetrical forms of benthic foraminifera and planktonic foraminiferal populations in a shallow-water sediment core obtained just off Kawar (14°49'43"N, 73°59'37"E) on the central west coast of India, which receives heavy river discharge during the southwest monsoon season (June to September) from the Kali and Gangavali rivers.
What was learned
Down-core plots of the data showed three major troughs separated by intervening peaks; and "since angular-asymmetrical forms and planktonic foraminiferal population are directly proportional to salinity fluctuations," according to Khare and Nigam, they say that "the troughs ... suggest low salinity (increased river discharge and thus more rainfall)," and that "these wet phases are alternated by dry conditions." They further report that the dry episodes of higher salinity occurred from AD 1320-1355, 1445-1535 and 1625-1660, and that the wet phases were centered at approximately AD 1410, 1590 and 1750, close to the ending of the sunspot minima of the Wolf Minima (AD 1280-1340), the Sporer Minima (AD 1420-1540) and the Maunder Minima (AD 1650-1710), respectively.
What it means
Although Khare and Nigam say that "providing a causal mechanism is beyond the scope of the present study," they note that "the occurrence of periods of enhanced monsoonal precipitation slightly after the termination of the Wolf, Sporer and Maunder minima periods (less sun activity) and concomitant temperature changes could be a matter of further intense research." We agree. The correspondences seem to be more than merely coincidental, especially when the inferences of the two researchers are said by them to be "in agreement with the findings of earlier workers, who reported high lake levels from Mono Lake and Chad Lake in the vicinity of solar minima," as well as the Nile river in Africa, which "witnessed high level at around AD 1750 and AD 1575."