ocean currents
the mass flow of water driven by wind and gravity
surface currents
wind driven movements of water at or near the ocean's surface
thermohaline
slow, deep currents that affect the vast bulk of seawater beneath the pycnocline; dependent on density (i.e., temperature and salinity)
wind
BLANK is main driving force of surface currents
10%
what percent of water in the ocean is involved in surface currents?
horizontally
in surface currents water flows BLANK in the uppermost 400 meters of the oceans surface; mainly driven by wind friction
Coriolis forces
Water "piles up" in the direction the wind is blowing; pressure increases on the "piled up" side; the force of gravity acts against the pressure gradient
right
coriolis effect causes surfaces currents to flow to the BLANK of the wind direction in the Northern Hemisphere
Left
coriolis effects causes surface currents to flow to the BLANK of the wind direction in the Southern Hemisphere
Ekman spiral
Underlying water layers move at an angle to the right (N. Hemisphere) of the overlying water until a depth of ~100 meters.....the result is called the BLANK also known as the net motion of the water
pressure gradient and Coriolis deflection
Balance between downhill urge of the BLANK and uphill tendency of BLANK and of course wind friction maintains and holds currents along the outside edges of the ocean basin.
Geostrophic gyres (Geos, "Earth"; strophe, "turning")
gyres in balance between the pressure gradient and the Coriolis effect
West Wind Drift (Antarctic Circumpolar Current)
is technically not a gyre because it does not flow around the periphery of an ocean basin
Western boundary currents
These are warm, narrow, deep, fast currents found at the western boundaries of ocean basins (eastern coasts of continents)
Western boundary currents
- The Gulf Stream
- The Japan Current
- The Brazil Current
- TheAgulhasCurrent
- The Eastern Australian Current
The gulf stream
is the largest of the western boundary currents Flow of >55sv, about 300 times the flow of the Amazon River
Eddy
a circular movement of water usually formed due to friction with adjacent waters/currents
eastern
BLANK boundary currents are not well defined, eddies do not form
Eastern boundary currents
These are cold, shallow, broad,slow and their boundaries are found at the eastern boundaries of ocean basins (western coasts of continents) - nutrient rich
Eastern boundary currents
-The Canary Current
-The Benguela Current
-The California Current
-The West Australian Current
-The Peru Current
Transverse currents
currents that flow from east to west and west to east; link western and eastern boundary currents
eastward
Westerly winds (weaker winds) drive BLANK transverse currents
westward
Trade winds (stronger winds) drive the BLANK transverse currents
West Wind Drift (or Antarctic Circumpolar Current)
The greatest of all ocean currents is the
westward intensification
Why should western boundary currents be concentrated and eastern
boundary currents be diffuse?
Wind-induced vertical circulation
is vertical movement induced by wind-driven horizontal movement of water.
Upwelling
is the upward motion of water. This motion brings cold, nutrient rich water towards the surface.
Downwelling
is downward motion of water. It supplies the deeper ocean with dissolved gases
Equitorial upwelling
water moving in currents on either side of the equator is deflected slightly poleward and replaced by deeper water (due to differences in Coriolis Effect at equator)
Coastal Upwelling
- Wind blowing parallel to shore, moves water
- Coriolis effect deflects water to right (N. Hemisphere) or left (S. Hemisphere)
- Ekman transport is offshore
- Surface water is replaced by water rising along the shore
-High biological productivity occurs
Coastal Downwelling
- Water driven towards the coastline will be forced downward, returning seaward along the continental shelf
- Supplies deep ocean with dissolved gases and nutrients
- Assists in distribution
of living organisms
- No direct affect on climate or productivit
El Ni�o:
the Southern Oscillation develops, the trade winds diminish and then reverse, leading to an eastward movement of warm water along the equator
surface waters of the central and eastern Pacific become warmer, and storms over land may increase
Occurs roughly
Thermohaline Circulation
� Slow, deep currents (below pycnocline) that affect the vast bulk of seawater; dependent on density (i.e., temperature and salinity)
� ocean is density stratified, with the densest water at the bottom.
There are five common water masses of thermohaline circulation
� 1) Surface water
� 2) Central water
� 3) Intermediate water
� 4) Deep water
� 5) Bottom water
Antarctic Bottom Water
- The densest water in the world
- Majority produced near Antarctic coast south of South America during winter
� Salt is concentrated in pockets between crystals of pure water and then squeezed out of ice as brine
� Very cold, very salty water! It sinks b
North Atlantic Deep Water
- Deep water is also formed in the northern polar
ocean, but must escape through deep channels
- Water formed in Arctic flows into the north Atlantic to form North Atlantic Deep Water
� Cold winds from Canada cool water and it sinks
Convergence zones
water masses run into each other and denser water slides underneath less dense water
Great Conveyor Belt
� Carries surface water to the depths and back again
� Formation of North Atlantic Deep Water north of Iceland, the water mass flows south through the Atlantic and then flows over (and mixes with) deep water formed near Antarctica
� These masses circumnav
Coriolis effect
Deep Water masses move very slowly relative to surface gyres, however, even at the slow speed BLANK modifies their pattern of flow!
gyres
-deflecting water into a circular pattern
-a circuit of mid-latitude surface currents
around the periphery of an ocean basin
There are 6 great circuits in the ocean; 5 are geostrophic gyres:
- 1) North Atlantic Gyre
- 2) South Atlantic Gyre
- 3) North Pacific Gyre
- 4) South Pacific Gyre
- 5) Indian Ocean Gyre
- 6) West Wind Drift (Antarctic Circumpolar Current)- is technically not a gyre because it does not flow around the periphery of an oc
sverdrup (sv)
The volume of water transported in ocean currents is measured in the BLANK
� 1 BLANK= 1 million m3 per second