Chapter 7: Ocean Circulation
El Nino Southern Oscillation
(ENSO)
What are the normal conditions for the Walker Circulation Cell?
- Air pressure across equatorial Pacific is higher in eastern Pacific. - Strong southeast trade winds. - Pacific warm pool on western side of ocean. - Thermocline deeper on western side. - Upwelling off the coast of Peru.
Why are western boundary currents are the largest and fastest currents?
- Convergence of trade winds intensifies effect, - The increasing strength of the Coriolis effect with latitude causes the offset of the geostrophic "hills" to the west of center in ocean gyres
Why are ocean currents important to study?
- Impact both Weather and Climate - Transfer heat from tropical to polar regions. - Distribute nutrients and scatter organisms. - Important in navigation. - Important in fishing. - Important for leisure activities such as sailing, scuba diving, sports fishing, swimming and canoeing.
What are the four interconnecting currents with different flow that make up the North Atlantic gyre?
- North Equatorial Current (equatorial current) - Gulf Stream (western boundary current) - North Atlantic Current (northern boundary current) - Canary Current (eastern boundary current)
Coastal upwelling can...
1. cool the air along the coast, cooling the coastal air and adding to fog 2. bring nutrients to the surface increasing biological productivity, as along the coast of California
For surface currents, only about _% of the wind's energy is transferred to the ocean surface.
2
El Niño warm phase occurs on average about every______ years • Highly ______ pattern and usually last _____ months.
2-10; irregular; 12-18
Subtropical gyres are centered around ______ degrees latitude.
30
The ______ ______ current is the only current to completely encircle the Earth and is also the ______ current that moves ______ water than any other current.
Antarctic Circumpolar; largest; more
The ______ ______ current is just a southern boundary current of each of the ______ ______ gyres.
Antarctic Circumpolar; southern hemisphere
The North ______ gyre brings ______ temperatures up along the ______ coast.
Atlantic; warmer; east
______ downwelling occurs because winds along the coast move water onshore due to Ekman transport.
Coastal
______ upwelling occurs because winds along the coast move surface seawater offshore due to Ekman transport.
Coastal
______ ______ occurs when surface waters move away from an area on the ocean's surface.
Current divergence
One of the two basic types of ocean currents, also known as the Thermohaline Circulation. Mainly driven by differences in density caused by differences in temperature and salinity, exhibit vertical AND horizontal motions, affect deep water BELOW the pycnocline (90% of ocean water), and are LARGER and SLOWER than surface currents.
Deep currents
______ occurs when surface currents ______ (come together), pushing the surface water downwards.
Downwelling; converge
______ is the vertical movement of surface water to the deeper parts of the ocean. It supplies the deeper ocean with ______ ______ like oxygen.
Downwelling; dissolved gases
______ ______ currents are found at the ______ boundaries of ocean basins.
Eastern Boundary
______ currents make up the eastern part of the gyre (deflected by land) and carry cool waters from high-latitude regions toward lower latitudes.
Eastern Boundary
The average net movement of surface water column set in motion by wind is known as ______ ______.
Ekam transport
Coastal winds can cause upwelling or downwelling due to ______ ______.
Ekman transport
At times this normal Walker Circulation Cell is disrupted and winds blow toward the center of the Pacific known as __ ______.
El Niño
The warm phase of ENSO. The effects of the Southern Oscillation, the lack of upwelling and warmer water, are called __ ______.
El Niño (the EN in ENSO) (it is an oceanic phenomenon).
During __ _____ events, tropical hurricane formation is generally ______ in the Atlantic Ocean; Indian monsoons are typically ______ than usual.
El Niño; supressed; drier
______ upwelling; upwelling in the open ocean
Equatorial
______ are currents driven by the trade winds (north equatorial or south equatorial) and travel westward along equator.
Equatorial currents
Who was the Norwegian explorer, who first noticed that Arctic ice moved at a 20- to 40- degree angle to the right of the wind?
Fridtjof Nansen (1861-1930)
______, ______, ______ ______ all influence surface current patterns.
Gravity, friction, Coriolis effect
the _____ _____ is the largest WBC.
Gulf Stream
What are two examples of Western Boundary Currents?
Gulf Stream, Kuroshio Current
______ are large, circular-moving currents (loops of water) that are driven by major wind belts.
Gyres
What happens when the normal conditions of Walker Circulation Cell is disrupted?
High pressure in eastern Pacific weakens Trade winds weaken and may even reverse themselves Warm pool migrates eastward Thermocline deeper in eastern Pacific Downwelling Lower biological productivity (El Nino)
What conditions does La Niña bring?
Increased pressure difference across equatorial Pacific Stronger trade winds Stronger upwelling in eastern Pacific Shallower thermocline Cooler than normal seawater Higher biological productivity
Sometimes the normal conditions of the Walker Circulation Cell return quickly and more intensely, in a process called __ _____.
La Niña (cool phase)
seasonal winds
Monsoons
The ______ ______ gyre is a series of four interconnecting currents with different flow characteristics and temperatures.
North Atlantic
_______ or ______ currents are driven by the prevailing westerlies and create easterly water flow across ocean basin.
Northern; Southern Boundary (Northern boundary currents in Northern Hemisphere • Southern boundary currents in Southern Hemisphere)
______ ______ are masses of water that flow from one place to another.
Ocean currents
What are the other factors that can cause upwellings?
Offshore winds (Move water away from the shore) Seafloor obstruction (Restricts the flow of water and causes it to rise to the surface) Coastal geometry change (Produces upwelling where a sharp bend in the coastline causes deep water to surface) Lack of pycnocline (Occurs in high latitude oceans) Antarctic Divergence
The North ______ gyre brings ______ temperatures down along the ______ coast.
Pacific; cooler; west
The depth of the ocean in which density begins to change drastically
Pycnocline
The change in pressure and winds over the tropical eastern and the western Pacific Ocean waters is called the ______ ______ and causes a lack of upwelling of cold nutrient rich water
Southern Oscillation (it is an atmospheric phenomenon) (ENSO - El Niño Southern Oscillation)
______ Gyres rotate in the ______ direction of subtropical gyres. They are ______ and ______ than subtropical gyres.
Subpolar; reverse; smaller; fewer
_____ ______ produces a topographic ______ of the sea surface - a hill of water as much as __ (___) high.
Subtropical convergence; elevation; 2 m (6.6 ft)
Ocean surface currents, and wind, redistribute the heat from the ______.
Sun
One of the two basic types of ocean currents. They are wind driven with primarily horizontal motion, make up 10% of ocean's water, and exist mostly ABOVE the pycnocline.
Surface currents
______ and ______ are the two basic types of ocean currents.
Surface; deep currents
______ is the vertical movement of cold, deep, nutrient-rich water to the surface. Stimulates high ______ ______ and creates a large amount of ______ ______.
Upwelling; biological productivity; marine life
The Ekam spiral model was developed by ______ ______, a Swedish physicist, in 1905.
V. Walfrid Ekman
______ currents make up the western part of the gyre (deflected by land) and carry warm waters from equatorial regions toward higher latitudes.
Western Boundary
_____ ______ is the tendency of warm western boundary currents of each subtropical gyre to be particularly strong, swift, and narrow.
Western intensification
Ekam Spiral
Wind-driven surface currents move at an angle to the wind (each successive layer moves increasingly right (N hem.)) due to Coriolis Effect
El Niño strongly affects ______ productivity and lowers it.
biological
Countercurrents along the equator occur because of the ______.
calm along the meteorological equator (air is rising and the trade winds do not blow across the boundary).
At times, the normal Walker Circulation Cell is disrupted and wind blows towards the ______ of the Pacific.
center
Ekman transport causes water to flow toward the ______ of the gyre. known as the converging flow or ______ convergence.
center; subtropical
The monsoon wind system, which _____ ______ with the seasons, dominates circulation in the Indian Ocean.
changes direction
Surface ocean currents directly influence the ______ of adjoining landmasses.
climate
Subtropical gyres flow ______ in the Northern Hemisphere and ______ in the Southern Hemisphere.
clockwise; counterclockwise
Salty, warm water is not as dense as ______, salty water
cold
Eastern boundary currents are always ______ and flow from _____ to ______.
cold; high; low
Eastern Boundary Currents tend to have opposite properties of WBC, ______, ______, ______, and ______.
cold; slow; shallow; wide
Cool ocean currents (such as the California current) ______ the air at the ______. Cool, dry air; Dry climate on adjoining landmass.
cool; coast
Western US is _____ and the eastern US is ______ because of the currents in gyres.
cooler; warmer
Equatorial currents are typically accompanied by ______, which flow on the surface in the opposite direction from the main current.
countercurrents (eastward flow)
In the Ekam spiral, The water under the current nearest to the surface is driven by the ______.
current above it
Along the equator, wind generated Ekman transport causes surface waters to ______.
diverge
When currents converge, water piles up and has no place to go but ______.
downward
Prevailing westerlies at 30-60º blow currents to the ______.
east
Eastern boundary currents move cold water ______.
equatorward
The primary driving force of surface currents is ______ between surface winds and the ocean surface.
friction
All the effects that influence surface current patterns (gravity, friction, Coriolis effect) as well as the distribution of continents, together lead to ______.
gyres
Eastern boundary currents (Canary Current) blow from ______ to ______ latitudes, and thus, are always ______.
high; low; cold
Thermohaline circulation originates in _____ latitudes at the ______ ______.
high; ocean surface
Ekman transport produces the "______" of water within subtropical gyres that causes _____ ______ flow
hill; geostrophic current
Regions of downwelling have ______ biological productivity because of the nutrients get used up and are not continuously resupplied by the cold, nutrient-rich water from below the surface
low
Western boundary currents (Gulf Stream) move from ______ to ______ latitudes, and thus, are always ______.
low; high; warm
The absence of a ______ allows significant vertical mixing between high-density cold surface water and high-density cold deep water below
pycnocline
Coriolis force pushes currents (and winds) to the ______ in the Northern Hemisphere and to the ______ in the Southern Hemisphere.
right; left
North of the equator, waters of the South Equatorial current turn to the ______. South of the equator, waters of the South Equatorial current turn to the _____. This causes nutrient rich deep water to flow up to replace surface water.
right; left
What are the three things Indian Ocean Monsoons affect?
seasonal land weather, seasonal Indian Ocean currents, and phytoplankton activity
Ekam spiral describes speed and direction of ______ ______ at different ______.
seawater flow; depths
Surface currents have ______ speeds than corresponding winds.
slower
The Coriolis effect causes ______ ______ under ideal conditions to move ____ to the ____ (in the Northern Hemisphere) of the direction of ______.
surface waters; ~45°; right; wind (Ekam spiral)
The Antarctic Circumpolar current is able to encircle the Earth due to ______.
the lack of land at high southern latitudes
Without Coriollis force, western and eastern sides would be ______. With Coriollis force, central hill is shifted ______. This ______ the western boundary current and _____ the eastern boundary current.
the same; westward; compresses; expands
Equatorial currents are driven by ______ winds.
trade
The most significant winds causing surface currents are ______ winds and ______ ______.
trade (0-30 degrees); prevailing westerlies (30-60 degrees)
This divergence of currents at the equator generates ______ and high productivity. It is called equatorial upwelling.
upwelling (nutrient rich water replaces surface water)
______ and ______ provide important mixing mechanisms between surface and deep waters and can occur in a variety of ways.
upwelling; downwelling
Downwelling surface water is ______ and nutrient-depleted .
warm
Warm ocean currents (such as the Gulf Stream) ______ the air at the _____. Warm, humid air; Humid climate on adjoining landmass.
warm; coast
Western boundary currents are always ______ and flow from _____ to ______
warm; low; high
Northern Europe is ______ because of the heat from the Gulf Stream/North Atlantic Drift.
warmer
Trade winds at 0-30º blow surface currents to the ______.
west
The top of the hill of water is displaced toward the ______ due to Earth's rotation.
west (Western Intensification)
The Antarctic Circumpolar current is driven by ______ winds.
westerly (westerlies)
If there were no continents, the ocean's surface circulation pattern would closely match the major ______ ______ of the world.
wind belts
Ekam transport is, theoretically (under ideal conditions), ____ to the movement of the wind.
~90° ~90° to the right in N. Hem. ~90° to the left in S. Hem.
