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Why are all of Earth’s named oceans considered one connected world ocean?

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Map graphic showing the boundaries of the five oceans-Pacific, Atlantic, Indian, Arctic, and Southern-using color-coded regions. Four different map projections are included: North Pole view, South Pole view, International Date Line view, and Greenwich Meridian view, each displaying the oceans' extents around the continents. — ocean Earth's oceans and their marginal seas cover nearly 71 percent of the planet's surface.

Earth’s named oceans are considered one connected world ocean because they form a single, continuous body of salt water contained within the planet's enormous basins. While humans divide this body into distinct regions—such as the Pacific, Atlantic, Indian, Arctic, and Southern oceans—these areas are functionally linked, as each demarcated ocean connects to at least two others.12

The physical reality of this interconnectedness is demonstrated by thermohaline circulation, often called the Global Ocean Conveyor. This system continuously transports seawater throughout all the named oceans, replacing surface water with deeper water and vice versa. Because of this constant movement and the lack of absolute barriers, the world’s oceans act as a unified reservoir that covers approximately 71 percent of Earth’s surface.231