ocean currents

eddy

• Small temporary loops of swirling water

• Can travel long distance before dissipating

• Swirling motion causes nutrients normally found in colder deeper waters to come to the surface

• Can range in size

ocean gyre

• Large system of spiralling circulations

• Thousands of miles in diameter

• Rimmed by large, permanent ocean currents

• Movement of the earth's major ocean gyres helps to drive the thermohaline circulation

gyre formation

• Form from:

  • Global wind patterns

  • Earth's rotation

  • Landmass

coriolis effect

• Earth rotates on an axis

• Circulating air deflected

  • Towards the right in the north

    • Clockwise currents

  • Towards the left in the south

    • Counter clockwise currents

eckmans spiral

• Beneath the gyre's surface current, the Coriolis effect results in an Ekman spiral

• Surface molecules move by force of the wind

• They drag deeper layers of water molecules below them

• Each layer below them moves slower than the layer above them

  • Causing the spiral affect

life in gyres

• Centres: typically nutrient poor and Lower levels of plankton and algae

• Increasing SST means the centre is expanding within the gyrre

thermohaline circulation

• Deep ocean currents driven by the difference in density of water

• Controlled by temp and salinity

• Salinity - haline

• Temp - thermo

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Leeuwin

• Second largest current in Australia

• Warm poleward flowing current

• Brings warm water from Indonesia, south around cape Leeuwin to South Australia

• Between the coast and south-west portion of the WA current

• Occurs because of the 'gap' between Aus and Indonesia connecting the pacific and Indian ocean

• Easterlies over the pacific pile warm, low salinity water over the ocean basin

• Less dense water causes increase in sea level though Indonesia

• Water flows to lower level

  • Transferred down coast of WA

• 'core' generally be detected as a peak in the surface temp

  • Strong temp decrease further off shore

• Surface temp difference across the current

  • 1 deg at north west cape

  • 2-3 deg at Fremantle

  • 4 deg at Albany

• Strength largely influenced by the southern oscillation index

• El Nino = weaker

• La Nina = stronger

• About 300m deep (effects)

• La Nina creates marine heatwaves

  • Coral bleaching, flooding, seagrass damage, deaths for temperate species

• Weakens seasonally - strongest during autumn and winter (best when southerly winds are at their weakest)

• Weakest during summer - monsoonal winds

• Brings low nutrients

• Pelagic productivity is much lower

leeuwin influence

• Distribution of marine life and WA's weather

• Transport of tropical marine species down the west coast

• Allows reef-building corals to exist in the Abrolhos islands

• Recruitment of fish species much higher due to currents strength

• La Nina when current strengthens:

  • More productivity

  • More juvenile recruitment of crayfish, herring, salmon, and pilchard

• Transports eggs and larvae of tropical and subtropical species

• Allows WA's unique environment

• Mass coral spawning due to intensification of current in march

• Tropical fish species travel further south due to warm water ??

• Humpback whale/ other migratory animals use the current to help migration patterns

weather impacts of leeuwin

• Strong current = warmer waters = more evaporation = more rain

• Weak current = cold water = less evaporation = little rain/drought

south equatorial current

• Part of the Indian Ocean Gyre

  • One of major oceanic gyres

• Warm, nutrition low currents

• Predominantly east to west direction

• Typically 10 - 20 degrees south

• Influences Indian ocean dipole

• Strong northward extension of the SEC during Positive IOD events can lead to warmer waters in western Indian ocean and cooler waters in the east, impacting monsoon patterns and rainfall over Australia

• Positive IOD + SEC = reduced rainfall in Australia

• Negative IOD + SEC = increased rainfall in Australia

entire ocean dipole

• Climate pattern in he Indian ocean

• Characterised by the differences in sea surface temperatures between the western and eastern tropical regions

• Positive dipole - warmer than average SST in the west and cooler averages in the east

• Negative dipole - cooler than average SST in the west and warmer SST in the east

• Neutral dipole - west and east temperatures close to the averages

western australian current

• Relatively cold surface current of southeast Indian ocean

• As south Indian current reaches Australia it turns north

• Eventually joins the south equatorial current

• Mainly seasonal

  • Weaker in winter

• Highly affected by winds

• When at it strongest (summer) winds tend to blow strongly

• Leeuwin currents work opposite

• Located further offshore due to the Leeuwin (nearshore)

• Large contributor to subtropical gyre

• Transports less water than most eastern boundary currents

• Brings greater amounts of nutrients during summer due to the strong southerly's creating upwelling