Chapter 7- Ocean Circulation
North Atlantic current
-The northernmost surface current of the North Atlantic Subtropical Gyre
Sargasso Sea
-is the water that circulates around the North Atlantic Gyre's center of rotation, which is shifted to the west because of Earth's rotation. -can be thought of as the stagnant eddy on the western side of the North Atlantic Gyre
Arctic convergence
A zone of converging currents similar to the Antarctic Convergence but located in the Arctic
Convergence of currents/surface water -When currents converge, water stacks up and has no place to go but downward. These areas are associated with low productivity
What causes downwelling?
Divergence of currents/ surface water
What causes upwelling?
Turbines that move in response to currents
What part of the ocean can be used as a source of energy?
Eastern Boundary currents
When currents flow back across the ocean basin, the Coriolis effect and continental barriers turn them toward the equator creating these currents -They come from high-latitude regions where water temperatures are cool, so they carry cool water to lower latitudes.
El Nino-Southern Oscillation (ENSO)
--The correlation of El Niño events with an oscillatory pattern of pressure change in a persistent high-pressure cell in the southeastern Pacific Ocean and a persistent low-pressure cell over the East Indies. -The periodic changes in winds and ocean currents, alternating between warm and cool phases causing cooler and wetter conditions in the southeastern United States and unusually dry weather in southern Africa and Southeast Asia.
Sargassum
-A brown alga characterized by a bushy form, substantial holdfast when attached, and a yellowbrown, green-yellow, or orange color. The two dominant species of macroscopic algae in the Sargasso Sea are S. fluitans and S. natans.
Labrador Current
-A cold surface current flowing south along the coast of Labrador in the northwest Atlantic Ocean
Alaskan Current
-A cool surface current that carries water in a counterclockwise fashion in the Gulf of Alaska.
geostrophic current
-A current that grows out of Earth's rotation and is the result of a near balance between gravitational force and the Coriolis effect.
Deep currents
-A density-driven circulation/ current that is initiated at the ocean surface by temperature and salinity conditions that produce a high-density water mass, which sinks and spreads slowly beneath surface waters
Temperature-salinity (T-S) diagram
-A diagram with axes representing water temperature and salinity, whereby the density of the water can be determined. -can be used to identify deep-water masses based on their characteristic temperature, salinity, and resulting density
Argo
-A global array of free-drifting profiling floats that move vertically and measure the temperature, salinity, and other water characteristics of the upper 2000 meters (6600 feet) of the ocean
Surface currents
-A horizontal movement of ocean water that is caused by wind and that occurs at or near the ocean's surface
Pacific Decadal Oscillation (PDO)
-A natural and cyclic pattern of ocean-atmosphere variability in the Pacific Ocean that lasts 20 to 30 years and influences sea surface temperatures. - May be responsible for the frequency of El Nino events
Tropical Atmosphere and Ocean (TAO)
-A scientific program that monitors the equatorial Pacific and studies how El Niño events develop.
Tropical Ocean-Global Atmosphere (TOGA)
-A scientific program that was initiated in 1985 to monitor the equatorial Pacific and study how El Niño events develop; predecessor to the TAO program.
Subpolar gyres
-A small, circular-moving loop of water that is centered at about 60 degrees latitude in both hemispheres. - rotate in an opposite direction of subtropical gyres and are driven by polar easterlies -rotate counterclockwise orientation in the Northern Hemisphere and clockwise in the Southern Hemisphere.
El Nino
-A southerly flowing warm surface current that generally develops off the coast of Ecuador around Christmastime. Occasionally it will move farther south into Peruvian coastal waters and cause the widespread death of plankton, fish, and other organisms such as marine mammals that depend on fish for food.
Somali current
-A surface current that flows north along the Somali coast of Africa during the southwest monsoon season. - can be reversed to flow south along Somali coast during northeast monsoon season
Antilles current
-A warm current that flows north seaward of the Lesser Antilles from the North Equatorial Current of the Atlantic Ocean to join the Florida Current. -passes alongside the atlantic side of west indies
Leeuwin Current
-A warm current that flows south out of the East Indies along the western coast of Australia. -produces a mild climate in southwestern Australia, which receives about 125 centimeters (50 inches) of rain per year. During El Niño events, however, the this current weakens, so the cold Western Australian Current brings drought instead.
Irminger Current
-A warm surface current that branches off from the Gulf Stream and moves up along the west coast of Iceland.
ENSO index
-An index showing the relative strength of El Niño and La Niña conditions. -which is calculated using a weighted average of atmospheric and oceanic factors, including atmospheric pressure, winds, and sea surface temperatures. -Positive ENSO index numbers indicate El Niño conditions, whereas negative numbers reflect La Niña conditions. Normal conditions are indicated by a value near zero, and the greater the index value differs from zero, the stronger the respective condition.
conveyer-belt circulation
-An integrated deep-water and surface current circulation pattern that resembles a large conveyer belt
North Atlantic Deep water
-Cold, dense water formed in the Arctic that flows onto the floor of the North Atlantic ocean. -A deep-water mass that forms primarily at the surface of the Norwegian Sea and moves south along the floor of the North Atlantic Ocean - is less dense than Antarctic Deep water, so it layers on top of it.
Oceanic Common water
-Deep water found in Pacific and Indian Oceans as a result of mixing of Antarctic Bottom Water and North Atlantic Deep Water
Atlantic Equatorial Countercurrent
-Equatorial counter current between North Atlantic Subtropical Gyre and South Atlantic Subtropical Gyre.
Antarctic Bottom Water (AABW)
-In southern subpolar latitudes, huge masses of deep water form beneath sea ice along the margins of the Antarctic continent. -Here, rapid winter freezing produces very cold, high-density water that sinks down the continental slope - this is the densest water in the ocean and it spreads into all of the world's ocean basins
western intensification
-Pertaining to the intensification of warm western boundary currents of each subtropical gyre that are faster, narrower, and deeper than their corresponding eastern boundary currents.
western boundary currents
-Poleward-flowing warm surface current on the western side of each subtropical gyre. -coriolis effect deflects these currents away from the equator because they can not cross the continent -They come from equatorial regions, where water temperatures are warm, so they carry warm water to higher latitudes
Walker circulation cell
-Pressure difference across air between South America and Indonesia causes the strong southeast trade winds to blow across the equatorial South Pacific. -high pressure and sinking air dominate the coastal region of South America, resulting in clear, fair, and dry weather. -On the other side of the Pacific, a low-pressure region and rising air create cloudy conditions with plentiful precipitation in Indonesia, New Guinea, and northern Australia.
California Current
-The cold eastern boundary current of the North Pacific Subtropical Gyre.
Benguela Current
-The cold eastern boundary current of the South Atlantic Subtropical Gyre.
Peru current
-The cold eastern boundary surface current of the South Pacific Subtropical Gyre.
Antarctic Intermediate Water (AAIW)
-The deep-water mass formed from sinking at the Antarctic Convergence -flows north at a depth of about 900 meters (2950 feet) beneath the warmer upper-water mass of the South Atlantic Subtropical Gyre
Biofouling
-The gradual accumulation of organisms such as algae, bacteria, barnacles, and protozoa on underwater equipment, pipes, and surfaces, corroding and impairing structures and systems.
North Atlantic Subtropic Gyre
-The large, clockwiseflowing subtropical gyre that exists in the North Atlantic Ocean
South Atlantic Subtropical Gyre
-The large, counterclockwise-flowing subtropical gyre that exists in the South Atlantic Ocean.
South Pacific Subtropical Gyre
-The large, counterclockwise-flowing subtropical gyre that exists in the South Pacific Ocean. - includes the South Equatorial Current, which flows westward into the western intensified East Australian Current. 13 From there, it joins the Antarctic Circumpolar Current (West Wind Drift) and completes the gyre as the Peru Current
Ekman transport
-The net transport of surface water set in motion by wind. Due to the Ekman spiral phenomenon, it is theoretically in a direction 90° to the right and 90° to the left of the wind direction in the Northern Hemisphere and Southern Hemisphere, respectively
North Pacific Current
-The northernmost surface current of the North Pacific Subtropical Gyre
Atlantic Meridional Overturning Circulation (AMOC)
-The part of conveyer belt circulation in the North Atlantic that includes both surface and deep currents. - It has been getting weaker due to melting of glacial ice
Monsoon winds
-The seasonal wind pattern of the Indian Ocean and southern Asia, -During winter, air over the Asian mainland rapidly cools, creating high atmospheric pressure, which causes the wind to blow from southwest Asia off the continent and out over the ocean. These northeast trade winds are called the northeast monsoon. During this season, there is little precipitation because the air associated with the high pressure over land is so dry -During summer, the winds reverse. Because of the lower heat capacity of rocks and soil compared with water, the Asian mainland warms faster than the adjacent ocean, creating low atmospheric pressure over the continent. As a result, the winds blow strongly from the Indian Ocean onto the Asian landmass, giving rise to the southwest monsoon, which may be thought of as a continuation of the southeast trade winds across the equator. During this season, there is heavy precipitation on land because the air brought in from the Indian Ocean is warm and full of moisture.
thermohaline circulation
-The vertical movement of ocean water driven by density differences resulting from the combined effects of variations in temperature and salinity; ---------produces deep currents
Brazil current
-The warm western boundary current of the South Atlantic Subtropical Gyre.
Kuroshio current
-The warm western boundary surface current of the North Pacific Subtropical Gyre
Subtropical convergence
-The zone of convergence that occurs within all subtropical gyres as a result of Ekman transport driving water toward the interior of the gyres. -causing water literally to pile up in the center of the subtropical gyre. Thus, there is a hill of water within all subtropical gyres that is as much as 2 meters (6.6 feet) high
Antarctic Circumpolar Current (West Wind Drift)
-This current encircles Antarctica and flows from west to east at approximately 50 degrees south latitude but can vary between 40 and 65 degrees south latitude. -driven by the powerful prevailing westerly wind belt, which creates winds so strong that these Southern Hemisphere latitudes have been called the "Roaring Forties," "Furious Fifties," and "Screaming Sixties." - the only current that circumscribes the Earth, and transports more water per unit time than any other current
South Equatorial Current
-Westward moving current below the equator. Between the equator and 20 degrees south. - part of the south atlantic gyre
equatorial currents
-Westward-flowing surface currents that travel along the equator in all ocean basins, caused by the trade winds. They are called North or South Equatorial Currents, depending on their position north or south of the equator
West Australian Current
-a cold current that forms the eastern boundary current of the Indian Ocean Subtropical Gyre; it is separated from the coast by the warm Leeuwin Current
East Wind Drift
-a surface current propelled by the polar easterlies, moves from an easterly direction around the margin of the Antarctic continent. -most extensively developed to the east of the Antarctic Peninsula in the Weddell Sea region and in the area of the Ross Sea
Agulhas Current
-a warm- western boundary current of the Indian Ocean gyre that carries some Indian Ocean water around the southern tip of Africa and into the Atlantic Ocean -mostly joins Antarctic Circumpolar current which gets rerouted into the gyre
North Equatorial Current
-an equatorial current that flows west across the Pacific just north of the equator -splits into the Antilles current and Carribean Current
Meanders
-are snakelike bends in the current that often disconnect from the current and form large rotating masses of water called vortexes (vortex = to turn), which are more commonly known as eddies or rings.
La Nina
-conditions opposite of El Niño prevail in the equatorial South Pacific; these events are known as ENSO cool phase -which are similar to normal conditions but more intensified because there is a larger pressure difference across the Pacific Ocean. This larger pressure difference creates stronger Walker Circulation and stronger trade winds, which in turn cause more upwelling, a shallower thermocline in the eastern Pacific, and a band of cooler than normal water that stretches across the equatorial South Pacific
cold-core rings
-consist of counter-clockwise spinning cone-shaped masses of cold water that extend over 3.5 kilometers (2.2 miles) deep. - may exceed 500 kilometers (310 miles) in diameter at the surface. The diameter of the cone increases with depth and sometimes reaches all the way to the sea floor, where cones have a tremendous impact on sea floor sediment - are associated with upwelling and marine life
warm-core rings
-contain shallow, bowl-shaped masses of warm water about 1 kilometer (0.6 mile) deep, with diameters of about 100 kilometers surrounded by cooler water - they remove large volumes of water as they disconnect from the Gulf Stream. -rotate clockwise - are associated with downwelling and lack of life
Equatorial countercurrent
-is a narrow, easterly flow of water that occurs counter to and between the adjoining equatorial currents. -A large volume of water is driven westward by the north and south equatorial currents and piles up water on the western side of an ocean basin near the equator, creating higher sea level there. As a result, this bulge of water flows downhill toward the east under the influence of gravity - they become more well developed with a larger equatorial region
Downwelling
-is the downward movement of surface water to deeper parts of the ocean. -is associated with much lower amounts of surface productivity but carries necessary dissolved oxygen to those organisms living on the deep-sea floor
Upwelling
-is the upward movement of cold, deep, nutrient-rich water to the surface; -This cold water, rich in nutrients, creates high productivity (an abundance of microscopic algae), which establishes the base of the food web and, in turn, supports incredible numbers of larger marine life like fish and whales.
Antarctic Convergence (Antarctic Polar Front)
-is where colder, denser Antarctic waters converge with (and sink sharply below) warmer, less-dense sub-Antarctic waters at about 50 degrees south latitude
gyre
-large, circular-moving loops of water shown in Figure that are driven by the major wind belts of the world
Antarctic Divergence
-the name for the divergence As the East Wind Drift and the Antarctic Circumpolar Current (West Wind Drift) flow around Antarctica in opposite directions, - here there is an abundance of marine life due to upwelling
East Australian Current
-the warm western boundary current of the South Pacific Subtropical Gyre
sverdrup (sv)
-unit used to express volume transport in ocean currents = One million cubic meters (35.3 million cubic feet) per second
Pacific Warm pool
A large wedge of warm surface water on the western side of the Pacific Ocean caused by trade winds
Florida current
A warm surface current flowing north along the coast of Florida that merges into the Gulf Stream. -world's fastest current
Ekman spiral
An ocean circulation model that explains why the result is a surface flow at 45 degrees to the right of the wind in the Northern Hemisphere. Water at increasing depth below the surface will drift in directions increasingly more slowly and to the right, until at about 100 meters (330 feet) depth it may move in a direction opposite to that of the wind.
-Other techniques used for measuring deep currents include identifying the distinctive temperature and salinity characteristics of a deep-water mass and tracking telltale chemical tracers. -Some tracers are naturally absorbed into seawater, while others are intentionally added. - Ex. Tritium and Clorofluorocarbons
Besides Argo what other ways are there to measure deep currents?
-The first method involves pressure gradients, which are the slopes caused by large scale bulges and depressions in the ocean's surface -A second method uses radar altimeters—such as those launched aboard Earth-observing satellites today—to determine the lumps and bulges at the ocean surface, which are a result of the shape of the underlying sea floor1 as well as current flow. -A third method involves a Doppler Flow Meter to transmit low-frequency sound signals through the water. The flow meter remains stationary and measures the shift in frequency between the sound waves emitted and those backscattered by particles in the water to determine current movement.
How can surface current be measured indirectly?
1.A drift current meter will be set afloat in the ocean, and it position will be measured over time to determine flow rate of the current. 2. A propeller-type flow meter will measure the current attached a stationary ship or pier.
How can surface currents be measured directly?
-For instance, warm ocean currents warm the nearby air. This warm air can hold a large amount of water vapor, which puts more moisture (high humidity) in the atmosphere. When this warm, moist air travels over a continent, it releases its water vapor in the form of precipitation. Continental margins that have warm ocean currents offshore typically have a humid climate. The presence of a warm current off the East Coast of the United States helps explain why the area experiences such high humidity, especially in the summer. Conversely, cold ocean currents cool the nearby air, which is more likely to have low water vapor content. When the cool, dry air travels over a continent, it results in very little precipitation.
How do Ocean currents affect climate?
During Southwest monsoon, winds blow water away from shore in the Arabian peninsula which causes upwelling and higher productivity in cooler waters surrounding Arabia - During the Northwest monsoon, the opposite happens
How does monsoon season affect productivity in Arabia?
Northern boundary currents/ Southern boundary currents
Prevailing westerlies cause these currents to direct ocean surface water in an easterly direction across an ocean basin. In the Northern Hemisphere, these currents comprise the northern parts and southern of subtropical gyres
Gulf Stream
The high-intensity western boundary warm-water surface current of the North Atlantic Subtropical Gyre that flows northward off the East Coast of the United States.
North Pacific Subtropical Gyre
The large, clockwise-flowing subtropical gyre that exists in the North Pacific Ocean. -includes the North Equatorial Current, which flows westward into the western intensified Kuroshio Current near Asia. The warm waters of the Kuroshio Current make Japan's climate warmer than would be expected for its latitude. This current flows into the North Pacific Current, which connects to the cool-water California Current. The California Current flows south along the coast of California to complete the loop. Some North Pacific Current water also flows to the north and merges into the Alaskan Current in the Gulf of Alaska
Carribean Current
The warm current that carries equatorial water across the Caribbean Sea into the Gulf of Mexico.
-The Coriolis effect increases toward the poles, so eastward-flowing high-latitude water turns toward the equator more strongly than westward-flowing equatorial water turns toward higher latitudes -If a constant volume of water rotates around the apex of the hill in Figure 7.8b, then the velocity of the water along the western margin will be much greater than the velocity around the eastern side
What are some explanations for western intensification
Offshore winds from land to sea, - seafloor obstruction like a tablemount, - or a sharp bend in the coastline - in high latitudes where there is no pycnoclines, upwelling and downwelling is abundant
What are some other causes of upwelling?
1.The high pressure along the coast of South America weakens, reducing the difference between the high- and low-pressure regions of the Walker Circulation Cell. 2.This, in turn, causes the southeast trade winds to diminish. In very strong El Niño events, the trade winds actually blow in the reverse direction. 3.Without the trade winds, the Pacific Warm Pool that has built up on the western side of the Pacific begins to flow back across the ocean toward South America, 4.The warm water usually begins to move in September of an El Niño year and reaches South America by December or January 5.As the warm water moves to the east across the Pacific, the low-pressure zone also migrates. In a strong to very strong El Niño event, the low pressure can move across the entire Pacific and remain over South America. The low pressure substantially increases precipitation along coastal South America. Conversely, high pressure replaces the Indonesian low, bringing dry conditions or, in strong to very strong El Niño events, drought conditions to Indonesia and northern Australia.
What are the steps of El Nino?
(1) the North Pacific Gyre, the South Pacific Gyre, the North Atlantic Gyre, the South Atlantic Gyre, the Indian Ocean Gyre - Rotate clockwise in Northern Hemisphere, and counterclockwise in the Southern hemisphere
What are the world's 5 subtropical gyres
-coastal winds create Ekman transport that moves water away from shore, causing upwelling of cool, nutrient-rich water. This upwelling increases productivity and results in an abundance of marine life, including small silver-colored fish called anchovetas (anchovies) that become particularly plentiful near Peru and Ecuador.
Why does Peru have so many fisheries?
Ocean currents
are masses of ocean water that flow from one place to another.
Canary Current
the cold eastern boundary current of the North Atlantic Subtropical Gyre - is a broad, diffuse southward flow that eventually joins the North Equatorial Current, thus completing the gyre.
coastal upwelling
the process by which wind causes coastal water to move away from the shoreline causing water to rise from below to replace the water moving away from shore. - In the northern hemisphere, if winds move southward on the west coast, this can happen. ex. san francisco
Equatorial Upwelling
the result of Ekman transport that causes surface water north of the equator to veer to the right (northward) and water south of the equator to veer to the left (southward). The net result is a divergence of surface currents along the geographical equator, which causes upwelling of cold, nutrient-rich water
coastal downwelling
wind blows water toward coastline, the water stacks up along the shoreline and has nowhere to go but down
