What do you think is the cause of the dip (i.e. decrease) in salinity around the equator?

The dip in salinity around the equator is primarily caused by the significant rainfall and river runoff typical of tropical regions. This heavy precipitation dilutes ocean water, reducing salinity levels. Additionally, the equatorial upwelling of nutrient-rich waters can bring deeper, less saline waters to the surface, further contributing to this decrease. Combined, these factors create a region of lower salinity in an otherwise saltier ocean.