Step 1: Explore ocean features
Use Ocean Features in WebGIS to identify ridges, trenches, shelves, and basins, then connect those features to tectonic plate movement.
Ocean Literacy Principle 1
Earth has one big ocean with many features
The ocean covers about 70% of Earth’s surface and is the planet’s defining physical feature. It is one connected body of water: named oceans help us describe different regions, but they form one global system. This principle connects geologic features, ocean-water properties, circulation, and watersheds.
Guiding question: How can very different ocean places still belong to one connected system?
Grades 6–8 conceptual alignment: Adapted from NMEA Ocean Literacy Scope and Sequence under CC BY-NC-SA 4.0.
What this principle means
Geologic features
The movement of Earth’s tectonic plates shapes ocean basins and the varied features of the seafloor.
Ocean basins include major seafloor features.
Ocean basins contain ridges, trenches, rift valleys, seamounts, islands, continental shelves, and other features. Many of these features are created and changed by the movement of Earth’s tectonic plates.
Ocean basins change over geologic time.
The size and shape of ocean basins have changed over geologic time and continue to change. New ocean crust forms at spreading centers, while older, denser crust is recycled into Earth at subduction zones.
Earth’s internal heat contributes to plate movement. Continents that were once joined later separated along rift valleys, forming the continents and ocean basins we recognize today, and the continents are still moving.
Properties of ocean water
Temperature and salinity influence seawater density, connecting the properties of ocean water to circulation.
Temperature, salinity, and density are connected.
About 97% of Earth’s water is in the ocean. Temperature and salinity affect seawater density: colder or saltier seawater is generally denser.
Ocean temperature changes through warming and cooling, including heating by sunlight and cooling through contact with ice. Evaporation and sea-ice formation can raise salinity, while rainfall, river inflow, and melting ice can lower it. Differences in density help drive deep ocean currents.
Ocean salts come from several Earth systems.
Salts enter the ocean through erosion of land, volcanic emissions, reactions at the seafloor, and material deposited from the atmosphere.
More dissolved salt lowers seawater’s freezing point. Seawater is also generally slightly basic, although its pH varies across places and over time.
Ocean circulation
Ocean movement connects distant places and links the ocean to the water cycle, watersheds, atmosphere, and land.
Different forces move ocean water.
Wind, together with Earth’s rotation, helps organize surface currents. Differences in seawater density help drive deep currents, while the gravity of the Moon and Sun produces tides. The shapes of ocean basins and continents help guide circulation.
Currents transport heat, nutrients, and organisms throughout the ocean, linking distant regions and shaping marine ecosystems and climate.
Gyres, upwelling, and currents redistribute life.
Wind and Earth’s rotation organize many surface currents into large gyres. Large subtropical gyres generally rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
Coastal upwelling is common along western coasts of continents, where it brings cold, nutrient-rich deep water into the sunlit surface ocean and supports primary producers. Currents also carry larvae and juveniles into new areas.
The water cycle and watersheds connect land and ocean.
Water moves between ocean, land, and atmosphere through evaporation, condensation, precipitation, runoff, and groundwater flow.
Rivers and streams carry freshwater, salts, sediments, nutrients, and pollutants through watersheds to estuaries and the ocean. Where freshwater and seawater mix, they can create density differences that influence local circulation.
Sea level changes as ocean volume changes.
Global sea level rises when land-based glaciers and ice sheets melt and when warming seawater expands.
Key ideas
- The ocean is one connected body of water.
- Moving tectonic plates shape ocean basins and seafloor features.
- Temperature and salinity affect seawater density.
- Wind, tides, Earth’s rotation, and density differences move ocean water.
- Currents transport heat, nutrients, and organisms.
- The water cycle and watersheds connect land, atmosphere, and ocean.
Teach this principle
Step 2: Explore why water moves
Compare temperature and salinity at different depths, then ask students how the resulting density differences can help move ocean water.
Step 3: Follow what gets transported
Use currents, Upwelling, Copepod, and Deep Currents to trace how heat, nutrients, larvae, and other organisms move between connected ocean regions.
Why this matters
This principle gives students an early introduction to systems thinking by showing that different places and features still belong to one connected ocean. It is foundational because later ideas about biodiversity, climate, migration, and human impact all depend on understanding connection.
What students should take away
Students should come away understanding that the ocean is not a set of isolated facts or separate places. It is one global system made of many distinct regions that are linked by movement, exchange, and change.
Classroom prompt: If two ocean regions look very different, what evidence shows that they still belong to one connected system?
Teach with Blue Biome
Explore this principle with the platform
WebGIS
Explore ocean basins and seafloor features, then compare temperature, salinity, and currents to investigate why ocean water moves.
Knowledge Graph
Trace how species, places, processes, threats, and opportunities are connected across the system.
Cards
Use cards to explore examples of movement, connection, and large-scale ocean processes.
Start here
Species
Follow a species across the system
Use swordfish to explore how one organism connects distant ocean regions.
Ecoregion
Compare two regions
Compare one highly productive region with a contrasting basin or gyre to highlight both difference and connection.
Opportunity
Explore a current or process
Use deep currents to discuss what moves through the ocean and how distant places influence one another.
Featured examples
Featured Species
Species
Copepod
Copepods show how currents transport small drifting organisms and help young marine life spread between connected ocean areas.
Species
Swordfish
Swordfish help explain the principle because they move through large parts of the ocean system rather than staying inside one region.
Species
Tiger shark
Tiger sharks show that wide-ranging predators depend on connections among coastal habitats, open water, and large-scale ocean movement.
Featured Ecoregions
Ecoregion
Arctic Ocean
Distinctive: This ocean is shaped by sea ice, cold water, and strong seasonal shifts in light and temperature.
Connected to the global system: It shows how ocean conditions help regulate climate and affect the limits of life-supporting environments.
Ecoregion
Mediterranean Sea
Distinctive: This semi-enclosed sea has high evaporation, relatively salty water, and restricted exchange through the Strait of Gibraltar.
Connected to the global system: Its salinity and density differences influence water exchange with the Atlantic, connecting ocean-water properties to circulation.
Ecoregion
Benguela Current
Distinctive: This eastern-boundary current brings cold, nutrient-rich water to the surface along southwest Africa.
Connected to the global system: It connects upwelling, productive food webs, and circulation between coastal waters and the wider Atlantic Ocean.
Featured Cards
Opportunity
Deep Currents
Deep Currents illustrate the principle by showing how water movement links distant parts of the ocean below the surface.
Opportunity
Upwelling
Upwelling shows how currents bring cold, nutrient-rich deep water into the sunlit surface ocean, supporting primary producers and connected food webs.