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Grade 10-11 (age 15-17)

Ocean Currents & Properties

Ocean Currents & Properties

Wind pushes the sea surface to make surface currents, and warm equatorial water and cold polar water circulate like a giant conveyor belt. Warm currents carry heat poleward, while cold currents bring cool water equatorward and can drive upwelling. With deep circulation from temperature and salinity differences, heat is redistributed globally and climate is regulated. Here you can adjust the equator–pole temperature difference and watch warm and cold currents strengthen.

Ocean's conveyor belt
🌊 Why do ocean currents flow?
①Wind pushes the sea surface, creating surface currents
②Warm equatorial water and cold polar water circulate
③Like a giant conveyor belt connecting the whole globe
Warm and cold current circulation
25°C
💡 Key observations
①Larger temperature difference → stronger currents
②Warm currents: carry heat poleward (→ milder climate)
③Cold currents: bring cold water equatorward (→ trigger upwelling)
Types of currents

Surface vs Deep circulation

ChartCurrent classification
ItemSurface currentsDeep circulation
Driving forcewind (atmospheric circulation)temperature/salinity (thermohaline)
Depthsurface to ~hundreds mhundreds to thousands m
Speedfastvery slow (centuries to millennia)
ExamplesKuroshio, Gulf StreamNorth Atlantic Deep Water
El Niño and La Niña
El Niño
eastern Pacific SST ↑ → trade winds weaken → upwelling decreases → abnormal weather
eastern equatorial Pacific SST 0.5°C+ above normal
La Niña
eastern Pacific SST ↓ → trade winds strengthen → upwelling increases → opposite pattern
opposite of El Niño — Korea tends toward harsh cold/snow
🌡️ Properties of seawater
①Temperature: decreases with depth (mixed layer / thermocline / deep ocean)
②Salinity: ~35‰ (psu) on average; high evaporation → high salinity, high precipitation → low
③Density: lower temp / higher salinity → higher density → sinking (drives deep circulation)
Worked Examples and Exam Practice
Example 1
Like the Kuroshio Current, what is a surface current that carries warm low-latitude water toward higher latitudes called?
1
A current that carries warm equatorial water toward higher latitudes is a warm current.
2
Conversely, a current carrying cold high-latitude water toward the equator is a cold current.
▸ Warm current
Warm currents carry heat poleward, making nearby climates milder.
Example 2
If seawater gets colder or saltier, how does its density change, and what circulation does that drive?
1
Lower temperature and higher salinity both make seawater denser.
2
Denser seawater sinks, driving the deep (thermohaline) circulation.
▸ Density rises → sinking → deep (thermohaline) circulation
Surface currents are driven by wind; deep circulation by temperature/salinity (density) differences.
CSAT-style
Which statement about ocean currents and seawater is correct?
①Surface currents are driven mainly by temperature and salinity differences
②During El Niño, the eastern equatorial Pacific surface warms above normal
③Upwelling reduces nutrients and worsens fishing grounds
④Cold currents flow from the equator toward high latitudes
⑤Deep circulation is faster than surface currents
▸ ② During El Niño, the eastern equatorial Pacific surface warms above normal
1
In El Niño the trade winds weaken and the eastern equatorial Pacific surface warms above normal.
2
Surface currents are wind-driven (①), upwelling brings up nutrients and improves fishing (③), cold currents flow from high to low latitudes (④), and deep circulation is very slow (⑤).
Summary
Ocean circulation core
wind → surface currents / temperature·salinity → deep circulation → global heat transport
atmosphere and ocean together redistribute energy and regulate climate
🎯 Exam Points
①Surface: wind-driven / Deep: thermohaline (T, S)
②Warm = warm low→high latitudes / Cold = cold high→low latitudes
③Upwelling: cold deep water rises → nutrient-rich → good fisheries
④El Niño: E. Pacific SST↑, trade winds↓ / La Niña: opposite
⑤Korea: Kuroshio branch + N. Korea cold current meet → "transition zone" — rich fishery
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Atmospheric Circulation
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Weather Phenomena
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