OCE1001 Ch 7 Ocean Circulation

The current in the northwestern part of the North Atlantic Subtropical Gyre that transports warm water toward the North Atlantic is called the __________.

Gulf Stream The Gulf Stream is a western boundary current in the North Atlantic Subtropical Gyre, and transports warm water away from the tropics.

What causes upwelling and downwelling?

Upwelling and downwelling help vertically mix deep and surface waters. Upwelling—the movement of cold, deep, nutrient-rich water to the surface—stimulates productivity and creates a large amount of marine life. Upwelling and downwelling can occur in a variety of ways.

To produce a surface current of 1.6 knots in the open ocean, a steady wind of _____ knots would be required.

80 1.6 knots is 2% of 80 knots.

The theoretical movement of surface water due to Ekman transport in the Northern Hemisphere is about __________.

90 degrees to the right of wind direction

What are the main surface circulation patterns in each ocean basin?

Antarctic circulation is dominated by a single large current, the Antarctic Circumpolar Current (West Wind Drift), which flows in a clockwise direction around Antarctica and is driven by the Southern Hemisphere's prevailing westerly winds. Between the Antarctic Circumpolar Current and the Antarctic continent is a current called the East Wind Drift, which is powered by the polar easterly winds. The two currents flow in opposite directions, and the Coriolis effect deflects them away from each other, creating the Antarctic Divergence, an area of abundant marine life due to upwelling and current mixing. The North Atlantic Gyre and the South Atlantic Gyre dominate circulation in the Atlantic Ocean. A poorly developed equatorial countercurrent separates these two subtropical gyres. The highest-velocity and best-studied ocean current is the Gulf Stream, which carries warm water along the southeastern U.S. Atlantic coast. Meanders of the Gulf Stream produce warm- and cold-core rings. The warming effects of the Gulf Stream extend along its route and reach as far away as northern Europe. The Indian Ocean consists of one gyre, the Indian Ocean Gyre, which exists mostly in the Southern Hemisphere. The monsoon wind system, which changes direction with the seasons, dominates circulation in the Indian Ocean. The monsoons blow from the northeast in the winter and from the southwest in the summer. Circulation in the Pacific Ocean consists of two subtropical gyres: the North Pacific Gyre and the South Pacific Gyre, which are separated by a well-developed equatorial countercurrent. A periodic disruption of normal sea surface and atmospheric circulation patterns in the Pacific Ocean is called El Niño-Southern Oscillation (ENSO). The warm phase of ENSO (El Niño) is associated with the eastward movement of the Pacific Warm Pool, halting or reversal of the trade winds, a rise in sea level along the equator, a decrease in productivity along the west coast of South America, and, in very strong El Niños, worldwide changes in weather. El Niños fluctuate with the cool phase of ENSO (La Niña conditions), which are associated with cooler than normal water in the eastern tropical Pacific.

Of the following surface currents, which one(s) transport large volumes of warm water to higher latitudes? Choose all that apply.

Brazil Current Kuroshio Current the Gulf Stream

Of the following currents, which ones are parts of the South Atlantic Subtropical Gyre? Choose all that apply.

Brazil Current West Wind Drift Benguela Current South Equatorial Current

How do deep-ocean currents form?

Deep currents occur below the pycnocline. They affect much larger amounts of ocean water and move much more slowly than surface currents. Changes in temperature and/or salinity at the surface create slight increases in density, which set deep currents in motion. Deep currents, therefore, are called thermohaline circulation. The deep ocean is layered based on density. Antarctic Bottom Water, the densest deep-water mass in the oceans, forms near Antarctica and sinks along the continental shelf into the South Atlantic Ocean. Farther north, at the Antarctic Convergence, the low-salinity Antarctic Intermediate Water sinks to an intermediate depth dictated by its density. Sandwiched between these two masses is the North Atlantic Deep Water, which has high nutrient levels after remaining below the surface for hundreds of years. Layering in the Pacific and Indian Oceans is similar, except there is no source of Northern Hemisphere deep water. Worldwide circulation models that include both surface and deep currents resemble a conveyer belt. Deep currents carry oxygen into the deep ocean, which is extremely important for life on the planet.

Of the following statements about deep-ocean currents, which is/are true? Choose all that apply.

Deep-ocean currents transport a volume of water equal to that of 100 Amazon-size rivers. Deep-ocean currents contain water with high oxygen concentrations. Deep-ocean circulation is referred to as thermohaline flow. Deep-ocean currents are important regulators of global climate. Deep-ocean currents are initiated near Antarctica and in the North Atlantic Ocean, where cold, dense water sinks.

Of the following statements about the Ekman spiral and Ekman transport, which is/are true? Choose all that apply.

Ekman transport is to the right of the wind direction in the Northern Hemisphere. The Coriolis effect causes surface waters to move at an angle relative to the wind direction. Ekman transport can result in both upwelling and downwelling. In the deeper layers of the Ekman spiral, water can move in a direction opposite of the wind direction.

One of the world's most powerful currents, located off the east coast of the United States, is the __________.

Gulf Stream The Gulf Stream is a western boundary current and is part of the North Atlantic subtropical gyre.

Of the following locations, where would upwelling be expected to occur? Choose all that apply.

In areas of diverging surface currents Where seamounts or tablemounts are present Where there is a sharp bend in a coastline

Of the following conditions, which is/are related to strong El Niño events? Choose all that apply.

Increased abundance of hurricanes in the eastern Pacific Ocean Higher sea levels in the eastern Pacific Ocean associated with warmer water Increase in sea surface temperatures and destruction of coral reefs in the eastern Pacific Ocean

What is the Walker Circulation Cell?

It is the path that air takes as it moves from high to low pressure, and back to high pressure, in the South Pacific under normal conditions.

The Gulf Stream transports warm water into the __________.

North Atlantic The Gulf Stream is a western boundary current that transports warm water from the tropics toward the North Atlantic.

A deep and powerful southward subsurface current that flows under the Gulf Stream in the North Atlantic is the __________.

North Atlantic Deep Water The North Atlantic Deep Water is a subsurface current that forms as a result of the sinking of cooler, denser water in the North Atlantic.

How are ocean currents measured?

Ocean currents are masses of water that flow from one place to another and can be divided into surface currents that are wind driven and deep currents that are density driven. Currents can be measured directly or indirectly by various methods.

Can power from currents be harnessed as a source of energy?

Ocean currents can be harnessed as a source of power. Although there is vast potential for developing this clean, renewable resource, significant problems must be overcome to make this a practical source of energy.

Indian Ocean currents that are generated by seasonal changes in weather patterns are the __________ and __________ Currents.

Somali/Southwest Monsoon In winter, northeast trade winds drive a North Equatorial Current westward just north of the equator, and part of that flow turns southward along the northeast African coast as the Somali Current. In summer, the trade winds are replaced by monsoon winds that blow from the southwest onto India/Asia. The North Equatorial Current is replaced by the eastward-flowing Southwest Monsoon Current, and the Somali Current reverses to "feed" the Southwest Monsoon Current.

The West Wind Drift is a part of which of the following subtropical gyres? Choose all that apply.

South Pacific Subtropical Gyre South Atlantic Subtropical Gyre Indian Ocean Subtropical Gyre

Of the following gyres, which one(s) flow in a counterclockwise direction? Choose all that apply.

South Pacific Subtropical Gyre South Atlantic Subtropical Gyre Northern Hemisphere Subpolar Gyres Indian Ocean Subtropical Gyre

What creates ocean surface currents and how are they organized?

Surface currents occur within and above the pycnocline. They consist of circular-moving loops of water called gyres, set in motion by the major wind belts of the world. They are modified by the positions of the continents, the Coriolis effect, seasonal changes, and other factors. There are five major subtropical gyres in the world; they rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Water is pushed toward the center of the gyres, forming low "hills" of water. The Ekman spiral influences shallow surface water and is caused by winds and the Coriolis effect. The average net flow of water affected by the Ekman spiral causes the water to move at 90-degree angles to the wind direction. At the center of a gyre, the Coriolis effect deflects the water so that it tends to move into the hill, whereas gravity moves the water down the hill. When gravity and the Coriolis effect balance, a geostrophic current flowing parallel to the contours of the hill is established. As a result of Earth's rotation, the apex (top) of the hill is located to the west of the geographical center of the gyre. A phenomenon called western intensification occurs in which western boundary currents of subtropical gyres are faster, narrower, and deeper than their eastern boundary counterparts.

What would you expect weather to be like on the eastern coast of Australia if the western coast of South America were experiencing unusually warm, wet weather?

The eastern coast of Australia would be experiencing unusually dry weather.

Of the following statements about subtropical gyres, which is/are true? Choose all that apply.

The western boundary current of all subtropical gyres is intensified (it is fast, narrow, and deep) The rotation of each subtropical gyre causes a "hill" of water to pile up within it. The centers of all subtropical gyres are associated with high atmospheric pressure. There are four main surface currents in each subtropical gyre. Globally, there are five subtropical gyres.

Of the following surface currents, which one(s) flow generally from west to east? Choose all that apply.

West Wind Drift North Pacific Current Equatorial Counter Current

The largest of the great ocean surface currents is the __________.

West Wind Drift Also known as the Antarctic Circumpolar Current, it completely circles the planet in the Southern Ocean.

Why does upwelling occur along the west coast of South America under normal conditions?

Winds moving westward in the South Pacific drive ocean currents toward the west; deep water rises to replace water driven westward.

The thermocline is _________________.

a steep temperature gradient in the ocean that separates deeper cold water from warmer upper water

During a strong El Niño event, the news media might be expected to cover __________.

a tropical cyclone in Hawaii or Tahiti Both Hawaii and Tahiti lie far enough from the equator that the water remains too cool to sustain a tropical cyclone-except when the body of warm water in the mid-Pacific expands to the north and south during an El Niño year.

To what depth in the ocean does the Ekman spiral extend?

about 100 meters (330 feet)

Surface ocean currents ___.

are driven by winds form large rotating gyres in the major ocean basins are influenced by Coriolis effect

Warm ocean currents ___.

are warmer than the surrounding water

When a meander from the Gulf Stream pinches off into the warm water south of the current, the eddy is called a __________.

cold-core eddy or ring

Downwelling can result from __________.

converging surface currents When currents bring water to a common area from several directions, water tends to "pile up". Gravity then causes it to sink, resulting in downwelling.

The loss of heat from the ocean surface, resulting in a lowered temperature, causes ocean water to become __________.

denser The cooling of water at the ocean surface causes the temperature to decrease, which, in turn, causes the water molecules to become more compacted (denser) and potentially sink.

Equatorial currents that are part of the subtropical gyres flow ___. Equatorial counter currents between the gyres flow ___ .

east to west; west to east

Which direction do ocean currents in the South Pacific move under El Niño conditions?

eastward

Ocean frontal systems that spin off from currents such as the Gulf Stream, akin to atmospheric storms, are known as __________.

eddies Eddies or water rings are sections of moving water that swirl off from the main Gulf Stream current and loop back on themselves, something akin to whirlpools.

Cool ocean currents ___.

generally flow from high latitudes towards the equator

A large system of rotating ocean currents, usually driven by the major wind belts, is called a(n) __________.

gyre An ocean gyre is any large system of rotating ocean currents. In the surface layer of the world ocean, there are five subtropical gyres and several smaller gyres.

What is the overall effect of the stronger than normal trade winds typical of La Niña conditions?

lowering of the South Pacific ocean temperature from normal conditions

Fluctuations in the flow of the Gulf Stream current result in curving loops of water known as __________.

meanders The Gulf Stream moves around in a wiggle-like fashion due to differences in densities between cold and warm water systems.

The subtropical gyres ___.

play a large role in climate

An indirect method of measuring ocean currents is the use of __________.

radar altimeters Radar altimeters measure irregularities in the ocean's surface that are caused by current flow (and also by bathymetric features). Current flow is calculated by mathematically modeling those effects.

Deep ocean currents ___.

result from changes in water density (due to temperature and salt content)

In the Northern Hemisphere, the Ekman spiral moves layers of water to the _____ of the wind direction and Ekman transport (the overall direction of water movement) is to the _____.

right; right

Records indicate that the ocean is warming faster in the Arctic polar regions than elsewhere. If that continues, a possible consequence could be __________.

slowing of deep ocean circulation, resulting in lower oxygen levels in deep water This is a concern of ocean and climate scientists for two reasons. Warming of the Arctic is causing glacial ice on the land areas to melt and increase fresh water flow into the ocean. Fresh water, being less dense, resists sinking. In addition (even if there were no change in salinity), warmer seawater does not sink as readily as cold water to feed the deep-water circulation, so the "conveyor belt" may slow down. The warmer water would contain less dissolved oxygen, which could limit the amount of animal life in both the deep ocean and in surface areas where deep ocean water upwells.

Thermohaline circulation in the ocean is driven primarily by differences in __________ and __________ among water masses.

temperature; salinity The term thermohaline (thermo = heat, haline = salt) refers to density differences among water masses mostly influenced by temperature and salinity.

What is the Southern Oscillation?

the swapping of high and low pressure zones in the South Pacific under El Niño conditions

Deep ocean current movement is also known as __________.

thermohaline flow Temperature and salinity are the two most important variables that determine the density of seawater.

Under which conditions are droughts and wildfires common in Australia?

under El Niño conditions

Warm core rings and cold core rings are associated with __________.

western boundary currents Only western boundary currents, particularly the Gulf Stream/Loop Current system, flow fast enough to produce turbulent flow.