Oceanography and World Regional Geography

Oceans cover most of the Earth’s surface and shape climate, trade, and biodiversity worldwide. This article covers the oceans and the continents they surround.

💡 Good to Know

Ocean Currents: Mechanics and Real-World Effects

• Ocean currents are driven by several forces together: prevailing winds at the surface, the Earth’s rotation (the Coriolis force, deflecting moving water), differences in water density from temperature and salinity, and the shape of ocean basins and coastlines.
• Tides Tides are the rhythmic rise and fall of ocean water about twice a day, caused by the gravitational pull of the sun and the moon. When the sun, moon and earth are in a straight line we get high spring tides; when the sun and moon are at right angles we get lower neap tides. High tides help ships enter harbours and help fishing.
• Currents Ocean currents are streams of water flowing constantly on the ocean surface in definite directions. Warm currents (like the Gulf Stream) start near the equator and move toward the poles; cold currents (like the Labrador Current) move from high latitudes toward the tropics. Where warm and cold currents meet are the world’s best fishing grounds.
• Primary Forces Four primary forces start a current moving: solar heating, wind, gravity, and the Coriolis force. Solar heating alone piles water up near the equator, about 8 cm higher than mid-latitudes.
• Gyres Coriolis force bends moving water into large, roughly circular current loops called gyres, one in each major ocean basin.
• Wind-driven surface currents move the upper ocean layer. Density-driven thermohaline circulation moves deep, cold, salty water along the ocean floor, together forming a global ‘conveyor belt’ of circulation.
• By the Numbers Surface currents, in the upper 400 m, make up only about 10% of ocean water. Deep water currents make up the other 90%, moving on density and gravity alone.
• Speed Currents are measured in knots and called by their “drift.” Surface currents can exceed 5 knots, while deep currents usually stay under 0.5 knots.
• Ocean currents don’t just affect marine life. They also significantly shape coastal climates, sometimes making nearby land areas warmer or cooler than their latitude alone would suggest.
• Tropical West Coasts Cold currents keep tropical and subtropical west coasts cool, narrow-ranged, foggy, and generally arid.
• Higher-Latitude West Coasts Warm currents give higher-latitude west coasts a marine climate: cool summers and mild winters with a narrow annual temperature range.
• Tropical East Coasts Warm currents flow along tropical and subtropical east coasts, giving these areas a warm, rainy climate instead.
• Cold, nutrient-rich currents rising from the deep ocean, called upwelling, fertilize surface waters and support some of the world’s most productive fisheries. The Peru (Humboldt) Current off South America sustains one of the largest fish catches on Earth this way.
• Where warm and cold currents converge, like off Newfoundland’s Grand Banks, nutrient mixing again boosts marine productivity. These convergence zones have historically supported some of the world’s richest fishing grounds.
• Coral reefs support disproportionately high biodiversity relative to the small area they cover, making their conservation a high-priority issue in ocean policy.
• “Superlatives in geography,” like the largest, highest, or deepest features on Earth, are frequently tested facts. But they only matter alongside understanding why those features formed where they did.

Wave Characteristics and Types of Tides, and Ocean Floor Relief: Major and Minor Features

• Crest and Trough The crest is a wave’s highest point; the trough is its lowest point.
• Height and Amplitude Wave height is the vertical distance from trough to crest. Amplitude is exactly half that height.
• Period and Wavelength Wave period is the time between two crests passing a fixed point. Wavelength is the horizontal distance between two crests.
• Speed and Frequency Wave speed, measured in knots, is how fast a wave moves through the water. Frequency is how many waves pass a point each second.
• Semi-Diurnal This is the most common pattern: two high tides and two low tides each day, of roughly equal height.
• Diurnal Here there is only one high tide and one low tide in a day.
• Mixed Tide These tides vary in height between successive highs or lows, seen along North America’s west coast and many Pacific islands.
• Ebb and Flow The falling period between high and low tide is called the ebb. The rising period between low and high tide is called the flow, or flood.

• Continental Shelf This is the shallowest, gently sloping edge of each continent, averaging 80 km wide and under 1° gradient. It ends at a steep drop called the shelf break.
• Continental Slope This connects the shelf to the deep ocean basin, with a steeper gradient of 2-5° and depths between 200 and 3,000 m.
• Deep Sea Plain These are the flattest, smoothest parts of the ocean floor, lying between 3,000 and 6,000 m deep and covered in fine clay and silt.
• Oceanic Deeps These trenches are the deepest parts of the ocean, 3-5 km deeper than the surrounding floor. Of the 57 explored so far, 32 lie in the Pacific, 19 in the Atlantic, and 6 in the Indian Ocean.
• Mid-Oceanic Ridge This is a pair of mountain chains split by a deep depression, with peaks up to 2,500 m. Iceland sits on the Mid-Atlantic Ridge.
• Seamount This is a volcanic, pointed-summit mountain rising 3,000-4,500 m from the seafloor without breaking the surface. The Emperor Seamount extends the Hawaiian Islands chain.
• Submarine Canyon These are deep valleys cutting across the shelf and slope, often at a river’s mouth. The Hudson Canyon is the best-known example.
• Guyot This is a flat-topped seamount, formed as a volcanic peak gradually subsides. Over 10,000 seamounts and guyots exist in the Pacific Ocean alone.
• Atoll This is a low, ring-shaped tropical island made of coral reef, enclosing a central lagoon.