The largest body of water on Earth depends entirely on how the term “body of water” is defined. While many people think of the named oceans, scientific understanding views these as interconnected regions of a single, massive entity. Therefore, the largest body of water is not a familiar named geographic feature but the Earth’s entire reservoir of saltwater. Understanding this concept requires examining the planet’s single, unified ocean, the relative sizes of its major basins, and the largest landlocked water bodies.
Defining the Unified Global Ocean
The single largest body of water is the World Ocean, or Global Ocean, a continuously circulating mass of saltwater covering approximately 71% of the Earth’s surface. This classification is rooted in hydro-connectivity, the physical link between all seemingly separate oceanic regions. Deep ocean currents and surface flows ensure a constant exchange of water throughout this vast reservoir.
This unified volume of saltwater holds about \(1.332\) billion cubic kilometers of water, representing over \(97\%\) of all the water on Earth. The traditional divisions into the Pacific, Atlantic, Indian, Arctic, and Southern Oceans are based on geographical and cultural boundaries, not true physical separations. The Global Ocean’s continuous nature means it acts as a single system that regulates global climate and weather patterns.
Ranking the Major Ocean Basins
While the Global Ocean is the single largest feature, the Pacific Ocean is the largest individual basin when the system is divided by conventional geographic boundaries. The Pacific covers more than \(30\%\) of the planet’s surface and is larger than the entire land area of all continents combined. It contains approximately \(50.1\%\) of the total volume of the World Ocean.
The Pacific Ocean spans roughly \(155\) million square kilometers in surface area, with a total volume estimated at over \(710\) million cubic kilometers of water. It is also the deepest on Earth, boasting an average depth of around \(4,000\) meters. The lowest known point, the Challenger Deep in the Mariana Trench, plunges to over \(11,000\) meters below sea level.
The Pacific Ocean’s volume is more than double that of the next largest basin, the Atlantic Ocean. The Atlantic, with a surface area of about \(85\) million square kilometers, is the second-largest, followed by the Indian Ocean.
Comparing the Largest Lakes and Inland Seas
A different category of water body is the inland sea or lake, defined by its landlocked nature and complete separation from the continuous flow of the Global Ocean. Within this category, the Caspian Sea holds the title of the largest body of water, measured by both surface area and volume. It is classified as an inland sea due to its large size and saline water content, though it is geologically a lake.
The Caspian Sea spans a surface area of roughly \(370,000\) square kilometers and holds a volume of approximately \(78,200\) cubic kilometers of water. It is a relict of the ancient Tethys Ocean, which explains its salinity. This massive landlocked feature is bordered by five different countries and is the largest closed basin on Earth.
Largest Freshwater Bodies
When considering only freshwater bodies, the largest is determined by the metric used for comparison. Lake Superior, located in North America, is the largest freshwater lake by surface area, covering about \(82,100\) square kilometers. Lake Baikal in Siberia, Russia, holds the title for the largest freshwater lake by volume, containing approximately \(22,995\) cubic kilometers of water due to its extraordinary depth.