Previously, such blobs of equatorial water were only discovered in the Pacific Ocean and the Indian Ocean, but not the Atlantic.

The initial stimulus may also appear in the ocean: if the thermocline deepens in the east or the temperature of upwelled waters rises (effects that can originate outside the tropics), upwelling ...

(It's always raining over an El Niño, and the rainwater dilutes the sea.) Both of these conditions contribute to buoyancy. A sharp temperature and density change—called the thermocline—floats ...