How should the ocean be divided?

Lesson overview

This lesson introduces students to the ocean environment and the various ways that it is classified, subdivided, or mapped in terms of biophysical characteristics. In addition, human-oriented divisions expressed in international policy are also shared. Despite these subdivisions, emphasis is placed on the ocean as a single interconnected system. Students should be encouraged to think about the advantages, disadvantages, and tensions between these different ways of mapping.

Learning outcomes
  • Describe the history of ocean exploration and the development of oceanography
  • Explain how the ocean is connected to other parts of the Earth
  • Identify and describe the different ways in which the ocean is divided
  • Discuss how a divided ocean might affect the ocean’s future
Lesson steps

1. How much do we know about the ocean? (10 minutes)

Use the slides to ask students to share their thoughts about the number of oceans and different ways to divide the ocean. Extend the discussion through popular culture references to the ocean and marine-related names.

When discussing the concept of oceans and seas, students might draw ideas from popular culture and common knowledge. These ideas might include:

  • The notion that there are 4+ oceans, which refers to the major world oceans such as the Pacific, Atlantic, Indian, Southern, and Arctic Oceans.
  • References to specific named oceans like the Atlantic and Pacific, which are well-known due to their vast size and prominence in geography lessons.
  • The concept of the "Seven Seas," a historical term that once referred to the primary bodies of water known to ancient civilizations.
  • The use of terms such as "High Seas" typically refers to the open ocean beyond territorial waters.
  • Named bodies of water that appear in popular culture or are geographically relevant, such as the Caribbean (famous from "Pirates of the Caribbean"), the English Channel, North Sea, Irish Sea, and Celtic Sea, among others.

2. The Rise of Ocean Understanding and Oceanography (15 minutes)

This section situates are naming and mapping conventions for the ocean within a historical context. Read through the Student Sheet and accompanying slides to consolidate student learning and then have students answer the questions on the Student Sheet. Review the answers using the slides and information on the Answer Sheet.

Students will cover the following main points:

  • The ancient Greeks and Romans had a basic classification of climate zones and named familiar bodies of water
  • Maritime exploration during the Age of Discovery (or Age of Encounter) expanded knowledge of the world
  • Important expeditions included Vasco de Gama, Christopher Columbus, and the first circumnavigations of the world
  • Non-European cultures, such as those in Asia and the South Pacific, were also significant maritime explorers
  • Explorers were motivated by the desire for wealth, prestige, and the establishment of trade routes and colonies
  • Later explorers during the Age of Enlightenment sought new resources, unexplored areas, and trade routes
  • The mid-nineteenth century saw the beginnings of scientific exploration of the ocean, leading to the development of oceanography
  • Advanced technologies in the twentieth century greatly enhanced our understanding of the ocean

3. The Ocean within the Earth System (10 minutes)

Although a consequence of the complex history of our understanding of the ocean has resulted in the ocean being subdivided into five ‘oceans’ (Atlantic, Pacific, Indian, Arctic, and Southern), modern science points to a better appreciation of the ocean as a single system.

This idea of a single and interconnected ocean is best revealed by the Spilhaus Projection. Share a side-by-side image of the Spilhaus Projection alongside a more traditional map of the world such as the Mercator or Peters projections. Ask students to compare and contrast these differing views of the world from what the projections show and how they might have been created, to how these different views may alter our appreciation of the centrality of the ocean to life on Earth. Question prompts for this discussion could include:

  • What are the main similarities between the two map projections?
  • What are the main differences between the two map projections?
  • How do the differences between the two shape your view of the ocean?
  • Do you think that one of the maps is more accurate than the other?
  • Do you think that one of the maps is more useful than the other?

As an extension, use the slides to extend this idea of an ocean system to incorporate a wider systems view of the planet that includes the atmosphere, geo- (or litho-) sphere, biosphere, and in some models the cryosphere. These represent planetary-scale ‘spheres’ of interacting subsystems of a single, interconnected planetary system giving rise to the new field of Earth System Science.

4. How should the ocean be divided? (20 minutes)

In this lesson step, students will work in small groups to study the different ways in which the ocean can be subdivided: geophysically (principally by depth and distance from shore), biologically (through different habitat types), and politically (through the exercise of control over areas of the ocean by nation states).

Hand out the three information sheets to students on how the ocean can be divided. Students should create a mind map of these different methods of dividing the answer, before deciding how they think the ocean should be divided.

5. Reflection and wrap-up (5 minutes)

Recap the main points of the lesson, Encourage students to consider the importance of understanding the interconnected nature of the ocean system and its role in the Earth system. Discuss the implications of human divisions of the ocean for resource management and conservation.