https://phys.org/news/2019-01-differentiating-summer-winter-rainfall-south.html

The marine sediment core known as 63KA was taken close to the mouth of the Indus River delta and holds important and intriguing information about past changes in river discharge and depth of ocean stratification. The discharge of the Indus River is directly linked to the amount of summer rainfall. Ocean mixing depth is related to the strength of winds and evaporation over the Arabian Sea during wintertime that, in turn, correlates with winter precipitation over northwestern India. Three species of planktonic foraminifera with distinct ecological niches have been used to track relevant changes in salinity and temperature by measuring the oxygen isotopes from their calcareous shells, which produce a synchronous record of summer and winter monsoon strength.

Work on samples from this marine core attracted wide interest in 2003 when a summer monsoon mega-drought around 4.2 thousand years ago was related to cultural transformations of the Indus Civilization, which had an urban phase spanning from c.4.5-3.9 thousand years ago.