week 5-ave Flashcards
what is the purpose of ocean currents
-help circulate heat and energy around the earth
-influence climate patterns around the world (rainfall, temperature patterns)
-transport sediments, pollutants
impact of current
- creates fertile fishing grounds in one area, ocean deserts in another
-marine productivity is linked to the movement of water around the world
gulf stream
picks up warm equatorial water to the east coast of USA
Wind driven currents
-interaction with the atmosphere is important because top 10% of water is where wind drives currents
-horizontal movement
density driven currents
-density driven currents are deeper
-vertical movement and mixing
-thermocline, pycnocline, hyocline
- salty and cold water is more dense in the poles and sinks to bottom
measuring ocean currents: direct
- tracking the movement of water by placing something in the water
- gps movement of drifting
-variable in flow direction and rate but measure overall pattern
drifting (direct)
-citizen science
-drift bottle and cards
- measures where the current ends up but not how it got there
drift current meter (direct)
-fixed point (poor spatial data)
-measures velocity of drift
propeller-type flow meter (direct)
- fixed or towed
doppler flow meter
-doppler means sound
-uses sound to measure current
-challenging due to interferences (animals, movement itself)
measuring ocean currents: indirect
- traceable junk
-location of incident and found object = path is inferred
what are the two examples from class about indirect currents
- may 1990 Nike shoes examples = they were washed overboard and each shoes’ individual serial number allowed them to be traced
-north pacific gyre
-plastic toy ducks washed over a ship and some were found in alaska, asia, and UK 12 years later
- the south pacific gyre played a role in this
measuring ocean currents: remote measurements
-rely on satellites, typically altimeter
-indirect measurement because they actually measure sea surface heights
what does satellite measurement tell us about ocean height and temperature?
-water piles just above and below the equator on the West pacific ocean due to transfer and forces pushing it that way
-surface winds move energy around, temperature changes tell us info on circulation
measuring deep currents
- free drifting submersible “floats”
-also measure temperature and salinity
-as of 2020 = 3932 floats globally
how much do ocean currents move?
??
-measured in sverdrups (Sv)
-1 Sv = 1 cubic hectometer per second
- a million meters cubed of water per second
what are the major ocean circulation patterns?
-equatorial currents, boundary currents, SH circumpolar current, Gyres
Western boundary currents
- fast moving, deliver warm water from the tropics up in to big bodies of water in the SH (push warm waters south)
western boundary currents history
- Benjamin Franklin tracked which ships were moving across the ocean the fastest
-fastest way from UK to NYC was to go up coast and then back down due to winds and drift - gyre system & trade winds = any ship going across the gulf stream was actually slower because they missed the current and wind
what was the gulf stream mission (1969)
-“the benjamin franklin”
-30 days
-travelled over 2,000km just on the drift
-started in miami west palm beach
Eddies
-eventually the W boundary current starts to dicipate and forms warm and cold water eddies
-these blips in the current are a loss of energy
-cold water = to the south
-warm water = to the north
-rapid drop in Sv indicates loss of water from current
if the eddie pinches off in cold water to the north…
the centre of the eddie is warm water
if the eddie pinches off in warm water to the south…
the centre of the eddie is cold water
kuroshio current
- north pacific
-western boundary current
-temperature difference = supports distinct population and warm water = nutrient poor
eastern boundary currents
- brings old water and transfers energy back down to the equator
-shallow, slow, and broad (1000km wide)
-poorly defined boundaries
-rarer eddies
-lower volume of water transported
features of eastern boundary current
-water is colder but more nutrient rich
-ex. Africa Benguela current = some of most productive waters
-connected to the circumpolar vortex
-cold water currents = nutrients
western vs eastern
eastern: tropical rainforest in the water but desert on land, very little moisture coming out of ocean when it is cold
western: tropical rainforest on land, desert in water
transverse currents
- they are driven by trade winds and westerlies
Currents that flow east → west – equatorial currents
west → east - northern/southern boundary currents
why is the fastest moving water at the top/near the surface?
-in closest contact with wind
-involves 10% of water in ocean
-occurs within and above the pycnocline
coriolos effect
-surface currents in the ocean
-northern hemisphere currents flow to the right of the wind direction (major wind belts)
-unlike winds, currents cannot flow over land, result = circular gyres in ocean as they hit off land masses
subtropical gyres (5)
ekman spiral *refer to slide
-ocean circulation model
-interplay between friction and coriolos effect
how coriolos generates upwelling?
-if the southernly winds are travelling up-coast, water is deflecting away
-creates almost a low pressure zone
-upwelling and minerals fills this low pressure zone
