Chapter 9-Ocean Circulation Flashcards
Canary Current
Northeastern Atlantic Ocean; southward flowing, cold-water, eastern boundary current. Begins where the mid-latitude currents are blocked by land. Runs south along the eastern edge of the Atlantic, carrying cold water to the equator. A single trip around this circuit takes about 10 years. Shallow, wider, edges not well defined.
Gulf Stream
Northwestern Atlantic Ocean; northward flowing, warm-water, western boundary current. Begins where the equatorial currents are blocked by land. Strong, deep, narrow, fast current. Moves away from the Equator, transporting large amounts of heat to the poles.
Kuroshio Current
Northwestern Pacific Ocean; warm-water, western boundary
California Current
Northeastern Pacific Ocean; cold-water, eastern boundary current
Brazil current
Southwestern Atlantic Ocean; warm-water, Western boundary current
Think about global conveyor belt/thermohaline circulation
Where strong upwelling does NOT occur
In regions where deep ocean water currents are formed (in other words, where cold salty water is sinking to the bottom)
During an El Nino event, how are currents affected?
A strong equatorial countercurrent develops in the Pacific
How many gyres are there? Where are they?
Name general patterns of surface circulation.
Five enormous gyres spin in subtropical waters, two in both the Atlantic and Pacific Oceans, and one in the Indian Ocean. Smaller polar gyres stir the northern Atlantic and Pacific. One surface current circles endlessly around Antarctica.
How do wind-driven currents work?
Currents are set in motion by winds and gravity, and steered by the placement of the continents and the rotation of the Earth. Wind is the most important cause of surface currents. When strong, sustained winds blow across the sea, friction drags a thin layer of water into motion.
The movement of the very topmost layer of the sea pulls on the water just beneath, which then in turn starts the layer under it moving. Energy from the wind is quickly dissipated, so wind-driven currents slow down with depth, and finally die out within a few hundred meters of the surface.
think about water height
How do currents affect the sea surface?
Surface currents are also triggered by gravity. The top of the sea is not flat but has broad hills and valleys. Where currents converge or run into a continent, water piles up. The major ocean gyres circle around a low mound a meter or so high. And in summer, intense sunlight can heat and expand seawater, raising the surface by several centimeters in the tropics.
What affects the direction of currents’ flow?
Currents run down these gentle slopes (created by differing water heights) under the pull of gravity. Winds and gravity start water moving, but the currents that form don’t flow parallel to the wind or straight down the steepest surface. Instead, the currents move at an angle to the force that generates them–a phenomenon called the Coriolis effect.
The Coriolis Effect occurs because the earth’s surface rotates faster at the equator than at the poles. It influences the paths of moving objects that are only loosely in contact with the ground, from currents to winds to airplanes. When objects move toward higher, slower moving latitudes, they outpace the rotation of the surface, and seem to veer toward the east. (If this plane left Miami heading straight at Chicago, it would miss its target unless it corrects for the Coriolis Effect.)
When objects move toward lower, faster moving latitudes, they lag behind the rotation of the surface. (This plane from Valparaiso veers toward the west and misses its destination of Santa Cruz by not adjusting for the Coriolis Effect.) The Coriolis deflection is to the right in the northern hemisphere, and to the left in the southern hemisphere.
The movements of currents are also constrained by the shape of the ocean basins. When a current runs into a continent, it must turn aside. The complex interplay between wind, gravity, Coriolis Effect, and topography determines the location, size, shape, and direction of the surface current gyres. (For example, consider this North Atlantic gyre. Like all the subtropical gyres, it is triggered by 2 of Earth’s prevailing winds–the trade winds and the westerlies.)
Western boundary current
The eastern and western currents of the gyre begin where the equatorial and mid-latitude currents are blocked by land.
What drives circulation, and what are the outcomes?
Give a very general description of circulation in the ocean
Global ocean circulation is driven by density variations in the ocean. Sometimes called thermohaline circulation because it depends on temperature and salinity, the conveyer begins on the surface of the sea near the poles. The conveyer belt begins at the surface of the North Atlantic where great amounts of water get very cold, chilled by low air temperatures, and then sink off the coast of Greenland. Hemmed in by the continents, this new deep water can only flow south, past the equator, all the way to the far ends of Africa and South America. As the current travels around the edge of Antarctica, fresh streams of cold water sink into and recharge the conveyer belt. Two sections split off and turn northward, one into the Indian Ocean, the other into the Pacific. Both these currents warm up and become less and less dense as they travel, enough that they eventually rise back toward the surface. Drawn by the inexorable pull of the conveyer belt, these now warm waters loop back the way they came and eventually return to the North Atlantic to begin the long journey all over again.
Ocean currents moderate the planet’s temperature extremes, with warm flows (like western boundary currents) carrying warm water from the tropics toward the poles, and codl flows (like eastern boundary currents) bringing cooler temperatures to low latitudes.
Where does upwelling occur?
Upwelling, the rise of deeper water to the surface, occurs only on 10% of the ocean. But that small area makes up half of the world’s fisheries. The cool, nutrient-filled water in upwelling currents support blooms of algae and seaweed, the base of the food chain for many clams, crustaceans, and fish.
Note that most upwelling occurs near coastlines - when winds running parallel to the coast drive surface water away from the continent due to Coriolis effect, upwelling occurs. Ex: in Northern Hemisphere along the western margin of continents when the wind blows towards the equator, Coriolis force causes the water to turn west and away from the coast; deep water rises up to replace the water that is moving away from the coast. Or in Northern Hemisphere along eastern margin of continents when wind blows toward poles. etc.
orgin; relationship to poles; relationship to cyclones
Westerlies (winds)
Prevailing winds that blow in an Eastern direction (NE in N.Hem and SE in S.Hem) between ~30-60° latitude (N/S). They originate from the high-pressure areas in the horse latitudes [or subtropical highs, subtropical latitudes w/high pressure between ~30°N/S {30-38°N/S} w/calm winds, low precipitation] and tend towards the poles and steer extratropical cyclones in this general manner.
Geostrophic flow
The horizontal movement of surface water arising from a balance between the pressure gradient force and the Coriolis force. Clockwise in N.Hem counterclockwise in S.Hem
Movement of ocean currents by gravity and modified by the Coriolis force is called __________
Geostrophic flow
Equatorial currents are driven by _________
the trade winds (prevaling Easterly wind pattern that blows East->West [twd SW in N.Hem and twd NW in S.Hem], found over tropical oceans in the area around the equator [~0-30°N/S]; Found within the lower portion of the Earth’s atmosphere, in the lower section of the troposphere [close to surface]; Strengthen during the winter and when the Arctic oscillation is in its warm phase; a result of high-pressure zones over the tropical and sub-tropical oceans, partly caused by relatively cool water - compared to warmer land air masses - located especially in the eastern half of the ocean basins. )
