Imagine you are a cosmic explorer on a long, interstellar voyage between your solar system and its closest neighbor. Your trusty and comfortable spaceship has carried you billions and billions of miles from home, yet for most of that trip, you’ve seen very little. Sure, that asteroid almost hit you, and your onboard computer developed a split personality half a parsec back, but other than that, your trip through interstellar space has been one of the most boring experiences of your thousand-year life.

Then, out of the corner of your telescopic viewscreen, a solar system with a strange blue dot appears. You do a systems check. All systems normal. Suddenly the dot increases to two pixels. And then more. Switching to ultrasupercalifragilistic high definition, you realize that the dot is a real object. It’s real! And it’s BLUE. Could there be something, a water-rich object, in this ghastly stretch of nameless space? Phone home, explorer. You just found a water planet!

Viewed from the far reaches of space, Earth, our home, looks like a tiny blue speck immersed in a sea of black. We know Earth looks this way because in 1990 a small spacecraft, Voyager 1, going where no manmade object had ever gone before, turned its camera back toward Earth and snapped a picture. In doing so, Voyager 1 captured a moment that has come to define what it means to be human. Deeply moved by this image, Carl Sagan (1934–1996), astronomer, author, and host of the original 1980 TV miniseries Cosmos, offered these words:

That’s here. That’s home. That’s us. On it, everyone you ever heard of, every human being who ever lived, lived out their lives. The aggregate of all our joys and sufferings, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there—on a mote of dust, suspended in a sunbeam. (Sagan and Druyan 1994)

The pale blue dot, as Sagan called it, is Earth, our home, the only known place in the universe where humans exist. Though small compared to the infinity of space, Earth remains our lone island, our singular port of call, a solitary outpost inhabited by the most fascinating and enigmatic species in the known universe, Homo sapiens. Earth is also the only known planet with liquid water covering most of its surface. Its pale blue color, visible from millions of miles away, comes from that water, the ocean—our world ocean.

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?

1.2 An Interdisciplinary Science

The scientific study of the world ocean, a field of science called oceanography, involves several different scientific disciplines. Generally, oceanographers identify with one of four major subdisciplines: 

• geological oceanography, the study of geologic processes in the ocean
• chemical oceanography, the study of chemical processes in the ocean
• physical oceanography, the study of physical processes in the ocean
• biological oceanography, the study of biological processes in the ocean

Oceanography also borrows from astronomy, geophysics, meteorology, physiology, ecology, and environmental sciences, to name a few. The integration of many different fields of science into one makes oceanography an interdisciplinary science, one that shares and integrates the tools and knowledge of many sciences. Though oceanographers tend to specialize in one discipline, their work requires them to be conversant in other sciences as well. They tend to dabble in multiple subjects, which is why an oceanography course can be so much fun—you learn a little of everything!

Oceanography also involves a host of non-scientist professionals, too, from technicians and programmers to a ship’s crew. Technicians provide an onboard repair shop for finicky instruments, programmers maintain the software that communicates with ocean sensors, and the crew navigate the ship, help deploy gear, and cook your meals. (A good rule to follow on board an oceanographic vessel? Be nice to the cook.) Without these support personnel, oceanography would be next to impossible. 

From a practical standpoint, oceanographers seek to understand the ways that the ocean serves humanity, how it provides what are called ecosystem services. Costanza et al. (1997) define ecosystem services as “the ecological characteristics, functions, or processes that directly or indirectly contribute to human well-being.” The ocean, for example, provides food, water, materials, waste purification, and a stable climate, among other things. Oceanographers want to know how human activities interfere with the services the ocean provides—how our actions affect the ocean’s ability to function properly and provide services to humanity. With more global-scale environmental and social challenges facing us than ever before, the stakes for understanding the ocean have never been higher.

1.3 An Earth Systems View

Humans exist in the web of a vast life support system controlled largely by the ocean. Much of the air that we breathe, the water that we drink, the food that we eat, and the climate in which we live originates from processes that operate within the ocean. While geologic forces ultimately contribute to slow changes in Earth’s climate, the ocean—in concert with other systems—dominates processes that affect climate on human timescales (e.g., decades to centuries). Together the various interdependent, interconnected systems that collectively regulate conditions on Earth have come to be known as the Earth system.

Loosely defined, a system consists of an assemblage of parts and processes working together. System parts include physical components—things composed of matter—while system processes refer to events or activities that result in some outcome. “Working together” implies interactions among those parts and processes—exchanges of energy and matter—and interdependency, meaning the parts and processes depend on each other. Systems may be simple or complex. Like molecules, they may exhibit emergent properties, characteristics and behaviors that cannot be observed by studying the individual parts separately. The properties of a water molecule differ markedly from the individual properties of hydrogen (a highly flammable gas) and oxygen (necessary for combustion). With emergent properties, the whole is greater than the sum of its parts.

A great number of systems surround and support you in your daily life. For example, a coffee maker is a fairly simple manmade system. It has parts (stand, filter, heater, etc.), the parts work together (coffee goes in the filter, the filter goes in the filter holder, water pours through the filter), there are regulatory processes for temperature and water flow (adjustable on pricier models), and the system produces a great-tasting end product: a cup of coffee. Yet it would be difficult to describe the taste of a cup of coffee simply by studying the parts of a coffee maker. 

Similarly, the human body consists of lots of subsystems: circulatory, nervous, musculoskeletal, urinary, reproductive, and more. But do these individual subsystems really describe you? Of course not. Each of you maintain your own beautiful self, despite the similarities of our bodily systems. 

1.4 Earth’s Seven Spheres

Though highly complex, the Earth system operates in much the same way as other systems with which we might be familiar. Within the Earth system, we can identify seven major subsystems, sometimes referred to as spheres (a reference to their names as well as the concept of their operation in a volume of Earth): 

• the heliosphere, the Sun and solar system
• the atmosphere, the gases surrounding Earth
• the geosphere, the solid Earth
• the cryosphere, the frozen parts of Earth
• the biosphere, Earth’s living systems
• the hydrosphere, Earth’s waters
• the anthroposphere, the human system

The hydrosphere includes the world ocean and all other waters upon or within Earth’s surface, including groundwater. The geosphere shapes the ocean basins and controls exchanges of energy and matter between Earth’s crust and the ocean. The atmosphere exchanges energy and matter between the atmosphere and ocean. In the frozen regions of the ocean, the cryosphere, when present, acts as a lid blocking the exchange of energy and matter between the ocean and the atmosphere. All subsystems interact with the Sun, part of the heliosphere, which supplies energy to Earth. Life on Earth constitutes what’s known as the biosphere, found from the uppermost reaches of the atmosphere to deep within Earth’s crust. One part of the biosphere, humans, have so radically changed our planet that scientists now consider human activities as a separate subsystem, the anthroposphere.

The description of the Earth system as a collective of seven spheres or subsystems is a useful model for understanding complex systems. Scientists call this a conceptual model, a sort of mental picture of how we think something works. Conceptual models guide our thinking and promote insights that can be tested by observation or experimentation. Our model of Earth as a system helps us appreciate the interconnectedness of its geological, chemical, physical, biological, and human processes. Perhaps most importantly, it helps us understand our utter dependency on this system for our survival. As so eloquently put in one of my favorite short documentaries, The Living Sea, “We live because the sea lives” (MacGillivray 1995). Conditions established by interactions among the seven spheres make Earth habitable for all living things.

1.5 The World Ocean System

The world ocean may also be viewed as its own system, the world ocean system. The geology, chemistry, physics, and biology of the ocean interact over nearly all scales of space and time. They’re all connected! In fact, the study of the world ocean as a system of interdependent parts and processes is what distinguishes oceanography from related disciplines, such as marine biology. Fundamentally, oceanographers aim to understand how the ocean works as a system. That’s why it behooves oceanographers to be familiar with other subdisciplines. Oceanographic research works best as an interdisciplinary science. We’ll visit this idea of an interconnected ocean system throughout the book. Indeed, it’s the book’s central theme. 

1.6 Keeping an Eye on Climate Change

Earth’s warming temperatures—global warming—and the consequences of that warming for Earth’s weather should concern every one of us. Nearly 100 percent of all climate scientists agree that humans are the cause of global warming. Yes, climate varies naturally. But human activities, especially the burning of fossil fuels and the chopping down of forests (i.e., deforestation), have sent Earth’s climate beyond its natural variations. Well beyond. Because we’re the cause, we have the capacity to be the solution. 

As you might expect, the ocean plays an enormous role in regulating the severity of the changes ahead. But before we go much further in our journey, it’s helpful to distinguish what scientists mean when they are talking about weather or climate.

Every day of our lives, we experience the changing conditions of the atmosphere, or what we call weather, the instantaneous state of the atmosphere in a particular location. Weather is happening right here, right now. Weather includes several different variables, such as temperature, humidity, clouds, precipitation, and wind. The ocean influences these variables.

As we grow older, we notice patterns in the weather; seasons change, some years feel hotter or colder, some seem wetter or drier. Seasonal, annual, decadal, and even longer timescale patterns in weather define what scientists call climate, the long-term statistics of weather conditions at a given location or globally. Climate represents the probability of a particular type of weather at a given time and place. For example, in California we normally expect hot, dry summers followed by cool, wet winters. Of course, any given day may be hot or cold in any season. But climate includes more than just the statistical average of weather conditions (e.g., average temperature or amount of precipitation). It also includes the type of weather event, its frequency and duration, and its intensity (Environmental Protection Agency 2021). Heatwaves, cold snaps, extreme floods, and droughts exhibit patterns over time that make up the statistics of climate.

A sports analogy can help us differentiate between weather and climate. A baseball player may get a hit or strike out in any given at bat. How they perform over a series of at bats defines their batting average. Hitters with a high batting average hit the ball more frequently. They may still strike out, but on average, they’re going to hit the ball more times than players with lower batting averages. Climate is like a batting average: it’s the weather we expect on average. Weather, however, like a given at bat, is what we get on any given day. A cold day in summer doesn’t mean winter has come. It’s just the weather for that day.

What worries scientists is that since the mid-1800s, Earth’s global climate has been changing faster than normal. Scientists refer to this as global climate change—changes in the statistics of weather conditions for the entire planet. Now, climate has been changing throughout Earth’s history. During the ice ages, much of North America and Europe was covered in glaciers. At other times, Earth has been so hot that the polar ice caps were completely melted. But the changes that brought these “icehouse” and “hothouse” conditions to Earth happened slowly, over the course of millions of years. The pace of change over the past several decades has no natural counterpart in Earth’s past. We hold the key to our climate future. And it begins with our appreciation and understanding of the Earth system. 

1.7 Ocean Literacy

In 2004, a group of more than 100 scientists, educators, policymakers, and ocean advocates met to discuss the most important ideas about the ocean. Based on those discussions, they published Ocean Literacy: The Essential Principles of Ocean Sciences (Ocean Literacy Network 2006) and later The Essential Principles and Fundamental Concepts of Ocean Sciences for Learners of All Ages (NOAA 2021). This document outlines seven major principles of ocean literacy, defined as “an understanding of the ocean’s influence on people and people’s influence on the ocean.” The Essential Principles of Ocean Sciences provides a road map for understanding our relationship with the ocean. The principles state:

1. The Earth has one big ocean with many features.
2. The ocean and life in the ocean shape the features of the Earth.
3. The ocean is a major influence on weather and climate.
4. The ocean makes Earth habitable.
5. The ocean supports a great diversity of life and ecosystems.
6. The ocean and humans are inextricably interconnected.
7. The ocean is largely unexplored.

This book adopts these principles and aims to develop in you an understanding of them. Like all science education, this effort is part of a global effort to improve science literacy, defined by the National Academy of Sciences as “the knowledge and understanding of scientific concepts and processes required for personal decision-making, participation in civic and cultural affairs, and economic productivity” (National Research Council 1996, 2013). Through a study of the ocean, you become not only an ocean-literate person but a science-literate one too. Your ability to “speak science” serves not only your interests but also the interests of the world. An ocean- and science-literate person uses their scientific knowledge and understanding to advocate sustainable use of the world ocean for the benefit of future generations.

1.8 Your Mission

Your mission, ocean explorer, if you decide to accept it, is to develop an understanding of our world ocean, the most important ecosystem on Earth. Through this understanding, I hope that you will dedicate yourself to becoming an ocean-literate person. In traveling these pages, I hope you will see how your life and the world ocean are intimately connected. Ultimately, I hope that what you learn here will inspire you to teach others about the world ocean. Together we can make our planet a more sustainable home for all beings, human and otherwise. As Sengalese conservationist Baba Dioum (b. 1937) so eloquently put it, “In the end, we will conserve only what we love; we will love only what we understand and we will understand only what we are taught” (Dioum 1968, as cited by Lotze 2020). 

I hope you’ll join me. Full speed ahead!

1.9 Chapter References

Anikouchine, William A., and Richard W. Sternbeg. 1973. The World Ocean: An Introduction to Oceanography.  Englewood Cliffs, NJ: Prentice Hall. https://archive.org/details/worldoceanintrod00anik

Carrington, Richard. 1960. A Biography of the Sea: The Story of the World Ocean, Its Life, and Its Influence on Human History. New York: Basic Books. https://archive.org/details/biographyofseat00carr

Costanza, Robert, Ralph d’Arge, Rudolf de Groot, Stephen Farber, Monica Grasso, Bruce Hannon, Karin Limburg, Shahid Naeem, Robert V. O’Neill, Jose Paruelo, Robert G. Raskin, Paul Sutton, and Marjan van den Belt. 1997. “The Value of the World’s Ecosystem Services and Natural Capital.” Nature 387: 253–260. https://doi.org/10.1038/387253a0

Cromie, William. 1962. Exploring the Secrets of the Sea. Englewood Cliffs, NJ: Prentice Hall. https://archive.org/details/exploringsecrets0000crom_i1o3/page/n7/mode/2up

Environmental Protection Agency. 2021. “Climate Change Indicators: Weather and Climate.” Updated May 12, 2021. https://www.epa.gov/climate-indicators/weather-climate

Giberne, Agnes. 1902. The Mighty Deep and What We Know of It. London: C. Arthur Pearson. https://doi.org/10.5962/bhl.title.18276

Harris, P. T., M. Macmillan-Lawler, J. Rupp, and E. K. Baker. 2014. “Geomorphology of the Oceans.” Marine Geology 352: 4–24. https://doi.org/10.1016/j.margeo.2014.01.011

Johnstone, James. 1923. An Introduction to Oceanography. Boston: Small, Maynard, and Company; Liverpool: The University Press of Liverpool.https://doi.org/10.5962/bhl.title.25450

Lotze, Heiki K. 2020. “Combining Love and Knowledge to Heal the Ocean.” Ethics in Science and Environmental Politics 20: 33–39. https://doi.org/10.3354/esep00193

MacGillivray, Greg, director. 1995. The Living Sea. Laguna Beach, CA: MacGillivray Freeman Films. Film, 40 minutes. https://www.imdb.com/title/tt0113676/

NASA. 2018. “Earthrise 1: Historic Image Remastered.” NASA Science, December 24, 2018. https://science.nasa.gov/earthrise-1-historic-image-remastered

National Research Council. 1996. National Science Education Standards. Washington, DC: The National Academies Press. https://doi.org/10.17226/4962

———. 2013. Next Generation Science Standards: For States, by States. Washington, DC: The National Academies Press. https://doi.org/10.17226/18290

NOAA. 2021. Ocean Literacy: The Essential Principles and Fundamental Concepts of Ocean Sciences for Learners of All Ages. Washington, DC: NOAA. https://www.marine-ed.org/ocean-literacy/overview

Ocean Literacy Network. 2006. Ocean Literacy: The Essential Principles of Ocean Sciences, K–12. Washington, DC: The National Geographic Society. https://www.aquariumofpacific.org/downloads/ed_SevenEssentialPrinciples.pdf

Pizer, Vernon. 1967. The World Ocean: Man’s Last Frontier. Cleveland and New York: World Publishing. https://www.google.com/books/edition/The_World_Ocean/O74z2lnoMZwC

Rather, Dan. 2017. What Unites Us: Reflections on Patriotism. Chapel Hill: Algonquin Books. https://www.workman.com/products/what-unites-us/paperback

Sagan, Carl, and Ann Druyan. 2011. Pale Blue Dot: A Vision of the Human Future in Space. New York: Ballantine Books. https://www.penguinrandomhouse.com/books/159735/pale-blue-dot-by-carl-sagan/

Shokalsky, Yu. 1917. Oceanography. Petrograd.

Spilhaus, Athelstan F. 1942. “Maps of the Whole World Ocean.” Geographical Review 32(3): 431. https://doi.org/10.2307/210385.

Vaughan, Thomas Wayland. 1937. International Aspects of Oceanography: Oceanographic Data and Provisions for Oceanographic Research. Washington, DC: National Academy of Sciences. https://doi.org/10.5962/bhl.title.16994

Wikipedia. 2023. “List of Seas.” Wikipedia, March 4, 2023. https://en.wikipedia.org/wiki/List_of_seas