1.1: A World Ocean Perspective

The world ocean covers 71 percent of the surface of our planet to an average depth of 2.3 miles (3.7 km). It includes all of the waters contained by the ocean basins—which cover 64.7 percent of Earth’s surface—and the waters that cover the edges of the continents—about 6.3 percent of the globe (e.g., Harris et al. 2014) . Myriad terms describe various parts of the ocean (seas and gulfs, straits and passages, bights and bays, harbors and sounds, banks and fjords), but oceanographers, the people, animals, and robots who study the world ocean, recognize only one ocean, the world ocean.

For convenience oceanographers call the three major ocean basins by their geographic names—the Atlantic, Pacific, and Indian Oceans. They also recognize two smaller oceans: the Arctic Ocean, an ocean basin surrounded by continents at the North Pole, and the Southern Ocean, a doughnut-shaped ocean defined by cold waters surrounding the Antarctic landmass. Of course, there are many geographic regions within the oceans: the Mediterranean Sea, the Gulf of Mexico, the Caribbean Sea, the Coral Sea, the Arabian Sea, the Red Sea, the Barents Sea, and numerous others. But these geographic designations disguise an important characteristic of Earth’s waters: they don’t stay in the same place for long. They don’t even stay in the same ocean basin. Water at one geographic location eventually—over timescales of hundreds of years—finds itself in another geographic location and even back where it began. The waters of the five major oceans flow between the basins and mix to form one ocean—the world ocean.

The idea of a world ocean, as opposed to several independent oceans, occurred to oceanographers at least a century ago, and likely much earlier. Scientific publications expressing the idea of a world ocean are difficult to find prior to 1917, but British author Agnes Giberne (1845–1939), who wrote novels and nonfiction (mostly with Christian themes), clearly states in 1902 her understanding of a world ocean:

In these days, we know the Ocean as one vast whole. . . . Minor oceans do exist, certainly. We have the Atlantic, North and South; the Pacific, North and South; the Arctic, the Antarctic, and the Indian. Yet for us there is but one great world-wide Ocean, encircling the Earth, every part being in connection with every other part. (Giberne 1902)

Giberne’s proclamation notwithstanding, various sources give credit for the term “world ocean” to Russian oceanographer Yuli Shokalsky (1856–1940), who used it in his 1917 monograph Oceanography. For English readers, Scottish oceanographer James Johnstone (1870–1932) used “World-Ocean” as the title of the first chapter in An Introduction to Oceanography, one of the earliest textbooks on the subject (Johnstone 1923). Johnstone mentions “the great Southern Ocean” and the “three Oceanic ‘Gulfs’ open out from the Southern Ocean.” The idea of the Southern Ocean at the “center” of the three major basins anticipates a modern view of the Southern Ocean as a kind of “steering wheel” for the world ocean circulation (Alfred Wegener Institute 2020).

World ocean thinking appears firmly embedded in oceanographic thinking by the 1930s. American oceanographer Thomas Wayland Vaughn (1870–1952) wrote in International Aspects of Oceanography (1937):

Just when the concept of the unity of all oceans originated is not easy to ascertain. As soon as it was recognized that the cold water in the depths of the oceans had come from Polar regions and that the renewal of the supply of water in those regions had come from other latitudes, the idea of a world ocean was born, and research was directed toward both the circulation within and the exchange of water between the different ocean basins.

South African American oceanographer Athelstan Spilhaus (1911–1998) put it even more succinctly in a paper titled “Maps of the Whole World Ocean” (1942):

Because it covers more than two-thirds of the earth’s surface, a map of the world ocean is essentially a world map. On ordinary world maps, the interruption forming the edges of the map are often placed in the oceans to show the continents to best advantage. If, on the other hand, oceanographic conditions as a whole are to be shown, it is desirable to have the map interrupted within the land masses and the world ocean shown as a unit.

By the 1960s, various authors had published books with “world ocean” in their titles or chapter headings, suggesting common usage of the term by this time (e.g., Carrington 1960; Cromie 1962; Pizer 1967). The first textbook to use the term in its title, The World Ocean: An Introduction to Oceanography (Anikouchine and Sternberg 1973), was the one I used in my freshman year at the University of Washington in 1974. The authors introduce the interconnectivity of the world ocean’s waters as the principle of unity. And they argue that a focus on memorizing the “names and placements of the continents and ocean . . . is slightly misleading because it suggests that the oceans are separated geographically. From an oceanographer’s point of view, the emphasis should be on a world ocean that is completely intercommunicating.” Of course, once the idea of a single world ocean is firmly embedded in your thinking, it doesn’t hurt to know the names and locations of at least some of the geographic oceans. How else will you know where to go when someone invites you to the Caribbean?