Scientists have discovered a previously undiscovered body of water in the Atlantic Ocean: a giant body of water that stretches across the Atlantic from the edge of Brazil to the Gulf of Guinea near West Africa. When ocean currents mix separate bodies of water to the north and south, a body of water called Atlantic Equatorial Water forms along the Earth’s equator.

Before the discovery of equatorial water in the Atlantic, scientists had observed water mixing along the equator in the Pacific and Indian oceans, but never in the Atlantic. The researchers published their findings Oct. 28 in the journal Geophysical Research Letters.

Ocean water is far from being the same everywhere; It is a huge patchwork of interconnected masses and layers that are mixed together and separated again by currents, eddies, and changes in temperature and salinity. Bodies of water are individual parts of this colorful arrangement; Each body of water shares a common geography, formation history, and common physical properties such as density and dissolved isotopes of oxygen, nitrate, and phosphate.

To distinguish between bodies of water, oceanographers plot the relationship between temperature and salinity in the ocean; These two measurements together determine the density of seawater.

In 1942, this picture of temperature and salinity led to the discovery of equatorial waters in the Pacific and Indian oceans. The equatorial waters of the Indian and Pacific Oceans, formed by the mixing of northern and southern waters, have temperatures and salinities curved along lines of constant density, easily distinguishable from surrounding waters. However, no such connection was observed in the Atlantic.

To find the missing body of water, scientists combed through data collected by the Argo program, an international array of self-submersible robotic buoys scattered throughout the world’s oceans.

After analyzing the data collected by this floating array, the researchers noticed an unseen temperature and salinity curve parallel to the curves marking the North Atlantic and South Atlantic, the central waters to the north and south, i.e. the Atlantic equatorial waters.

Now that the body of water has been identified, it will allow scientists to better understand the ocean mixing processes that are vital for oceans to transport heat, oxygen, and nutrients around the world.