Oceans and Life

The ocean floor, waves, tides and currents, tsunamis and cyclones, maritime zones and the Blue Economy.

Key ideas

• The ocean floor has the continental shelf, the steep continental slope, the flat abyssal plain, deep trenches and underwater mountains such as seamounts and guyots.
• The Mariana Trench is the deepest place on Earth, and the Mid-Ocean Ridge is the longest mountain range.
• A wave’s high point is the crest and its low point the trough; waves carve caves, arches and stacks and build beaches.
• Spring tides, when the Sun, Earth and Moon are in a line, have the biggest range; neap tides, at quarter moons, the smallest.
• Currents are driven by winds, the Coriolis force, differences in temperature and saltiness, and the shape of the basins; where warm and cold currents meet, fishing is rich.
• Tsunamis are giant waves caused mainly by undersea earthquakes; India’s warnings use seismic stations, ocean-bottom recorders and tide gauges.
• The Blue Economy means using the ocean for growth and jobs while keeping it healthy.

Remember

Watch out

• Mixing up spring tides (biggest range) and neap tides (smallest): spring tides have nothing to do with the season.
• Using nautical miles as kilometres: multiply by 1.852 to convert.
• Thinking tsunamis are caused by wind: most come from undersea earthquakes.

Worked example