Week 3 - ocean and ocean currents,

Warm currents

• Originate near the equator

• Carry warm water towards poles

• Found on the western side of ocean basins

• Warm currents raise temperatures of nearby coastal regions

• Increase humidity and precipitation

Important warm currents

• Gulf Stream

• Kuroshio

• East Australian current

Cold currents

• Originate from polar or deep waters

• Carry cold water towards the equator

• Found on the eastern side of ocean basins

• Cold currents cool adjacent land areas

• Often create dry coastal climates and fog

Important cold currents

• Peru current (Coast of Peru is cold because of the Peru current, cold surface of ocean means no rising of hot air, so no condensation)

• Benguela current

• California current

Meanders and Eddies

Black current

Warm and biologically unproductive, not a lot of nutrients so not a lot of fish

Causation of ocean circulation

• Caused by wind

• Caused by prevailing winds (eg trade winds, westerlies)

• Affected by the Coriolis effect (deflects moving water - right in northern hemisphere, left in southern)

• Continental boundaries (redirect currents)

Upwelling

• Caused by winds + Coriolis effect

• Brings cold, nutrient-rich water to the surface

• Lowers sea surface temperatures → cools nearby air

• Encourages dry conditions but support rich fisheries

Ocean heating up land **

• Land doesn’t cool off or warm up adjacent to the ocean, makes the ocean irrelevant to local land climate

• Ocean takes a lot of energy to warm up

• Lots of mixing of surface water

• Takes even longer to heat up

Water characteristics

• Highly polar: negative charges on one side, positive on the other → makes it easier for water molecules to attract each other (negative attracts positive)

• Temperature: water freezes at 0 degrees celius (273.16 degrees K), boils at 100 degrees Celsius

• High specific heat capacity: requires high amount of heat to heat up 1 gram of a substance by 1 degree Celsius

• Light penetrates oceans (doesn’t just get absorbed at surface)

• The upper ocean undergoes mixing so heat is not trapped at surface only (unlike land)

• Evaporation uses up energy that would otherwise go into heating ocean

Ice characteristics

• High latent heat of fusion, the energy required to melt ice

• Ice is less dense than water

• Because fixed crystal structure of ice takes up more space than liquid structure of water

• Highest density occurs at 4 degrees Celsius

Dissolved salts

• Main one is sodium chloride (NaCl, common salt)

• Mostly breaks up into ions (Na+ and Cl-) in water

• Dissolved salt tends to reduce “stickiness” of water molecules, thereby lowering the freezing point (sea water freezes at -1.9 degrees Celsius)

Sources of dissolved salts

• Earth’s crust

• Outgassing from mantle (“excess volatiles”)

• Most salts enter oceans from rivers and streams and leave ocean through deposits of sediments; the rest comes from ocean floor vents

Salinity (salt content)

• Salinity low near land (fresh water run off from rivers and melting glaciers)

• Salinity low near polar regions (low evaporation, precipitation, snow and ice melt)

  • Salinity low near equator (daily showers)

• Measured in parts per thousand

• Ocean well-mixed but salinity not uniform; some oceans more saline than others

El Niño-Southern Oscillation (ENSO)

Natural climate cycle characterised by the periodic warming (El Nino) and cooling (La Nina) of the central and eastern tropical Pacific Ocean’s sea surface waters, along with changes in the overlying atmosphere’s pressure

Neutral phase

• Easterly trade winds in the Pacific

• Leads to upwelling and cooler temperature in the East Pacific

• The warmer surface waters are pushed to the west

• Associated atmospheric circulation called the Walker Circulation

El Niño

• Trade winds weaken

• Reduces upwelling of cool water in the east Pacific Ocean

• East region becomes warmer

• West Pacific becomes cooler, associated with weaker trade winds

• Movement of warmest ocean regions causes displacement in Walker Circulation

La Niña

• Trade winds are stronger

• More upwelling

• Neutral conditions are magnified

Tides

Other types of ocean waves include wind-driven water waves

Waves

Oscillations that form along the interface between fluids of different characteristics, if there is relative motion between the two

Ocean wave types:

• Wind-driven waves are the most common

• Tsunamis sometimes incorrectly called “tidal waves”; caused by underwater land movements

• Tide waves (or just “tides”)

Spring Tide

have the highest high tides and lowest low tides, occurring when the Sun, Earth and Moon are aligned during New Moon and Full Moon phases.

Neap tide

Have the smallest difference between high and low tides, happening when the Sun and Moon are at right angles to Earth during the First and Last Quarter Moon phases