Oceanographers have found a new water mass in the Atlantic Ocean near the equator. For years, they believed the Atlantic lacked a true equatorial water mass, unlike the Pacific and Indian Oceans. Instead, it was thought that waters there were an extension of South Atlantic Central Water. Now, using temperature and salinity data from thousands of Argo floats, researchers have discovered a clear and consistent water pattern in the top 2,000 metres, especially near the equator. This water mass differs from known types. Named Atlantic Equatorial Water, it sits between 150 and 500 metres deep in the thermocline zone. This layer shows gentle temperature changes with depth, setting it apart from surrounding waters. Unlike other water masses formed at the surface, this new water mass forms by mixing. It mainly combines South Atlantic Central Water with a smaller amount of North Atlantic Central Water. The mixing happens in the equatorial current system where eastward and westward flows overlap, creating a stable water signature. This water mass stretches narrowly around the equator. It is separated from nearby waters by temperature and salinity fronts that follow the South and North Equatorial Currents. This helps keep its unique properties intact. Recognizing Atlantic Equatorial Water fills a gap in understanding ocean waters and improves knowledge of heat and salt movements in the Atlantic. The study was based only on temperature and salinity data. Future research using oxygen and nutrient levels may verify these results. This discovery shows even well-studied oceans can hide new secrets when examined closely.