Chapter 9

Where are the large gyres of the world ocean located?

North and South Pacific, North and South Atlantic, Indian Ocean, and the West-Wind Drift (Antarctic Circumpolar Current).

Antarctic water flows ____ _____ as ______ as the water in _______ ________

many; times; slowly; surface; currents

How many water masses are there?

5

What is a gyre?

A gyre is a circuit of wind-driven current flow around the periphery of an ocean basin

Where will the antarctic bottom water be 600 years from the antarctic

Aleutian islands

What are equatorial currents?

Equatorial currents are currents that flow on the surface in the OPPOSITE direction from the main current

What drives the vertical movement of ocean water? What is the general pattern of thermohaline circulation?

Gravity drives thermohaline circulation -- the slow circulation of water at great depths is driven by density differences rather than by wind energy. The whole ocean is involved in slow thermohaline circulation, a process responsible for the large-scale vertical movement of ocean water and the circulation of the global ocean as a whole.

How might weather in the western United States be affected by El Nino?

Greater evaporation of water from the warm ocean surface, combined with an increased number of winter storms steered into the western United States by a southward-trending jet stream, can double rainfall amounts and increase coastal erosion.

What are the names of the two major types of ocean currents?

Surface Currents and Thermohaline Currents

What causes the two major types of ocean currents?

Surface currents; are wind-driven movements of water at or near the ocean's surface, and thermohaline currents; are the slow deep density-driven currents that affect the vast bulk of seawater beneath the pycnocline.

Name a eastern boundary current

The California current

Name a western boundary current

The Gulf Stream

What is an example of a western boundary current?

The Gulf Stream

The flow direction of surface ocean currents is due primarily to

The Wind

Where are distinct water masses formed?

The characteristics of each water mass are usually determined by the conditions of heating, cooling, evaporation, and dilution that occurred at the ocean surface when the mass was formed.

Which way does wind typically blow over the tropical Pacific? How does wind flow in the tropical Pacific change during an El Nino event?

The trade winds blow from the normally high-pressure area over the eastern Pacific (near Central and South America) to the normally stable low-pressure area over the western Pacific (north of Australia). However, for reasons that are still unclear, these pressure areas change places at irregular intervals.

How is the Coriolis effect involved in the equatorial up welling?

Though the Coriolis effect is weak near the equator (and absent at the equator), water moving in the currents on either side of the equator is deflected slightly poleward and replaced by deeper water (Figure 9.15). Thus, equatorial upwelling occurs in these westward-flowing equatorial surface currents.

In the North Pacific (Northern Hemisphere), Gyre surface currents flow in a clockwise direction. True or False

True

How does thermohaline circulation force the thermohaline toward the oceans surface?

Water sinks relatively rapidly in a small area where the ocean is very cold, but it rises much more gradually across a very large area in the warmer temperate and tropical zones. The continual diffuse upwelling of deep water maintains the existence of the permanent thermocline found everywhere at low and mid-latitudes.

Eastern boundary currents: a. are located east of the continents. b. carry cold water toward the equator. c. are difficult for sailors to navigate. d. are relatively deep, narrow and fast.

c. are difficult for sailors to navigate.

Warmer water causes more ________ and ___ atmospheric pressure

evaporation; low

An eastern boundary current is generally narrow and swift. True Or False

False

What are water masses? What determines their relative position in the ocean?

A water mass has distinct temperature and salinity characteristics. The relative positions of water masses depend on their densities. Water masses don't often mix easily when they meet due to their differing densities; instead, they usually flow above or beneath each other.

During a major ENSO event water can rise by as much as ____ cm int the Galapagos

20

How many years will it take for antarctic bottom water to reach the currents

1,600

What percentage of the world ocean is involved in wind-driven surface currents?

10%

What is the Southern Oscillation? How is this related to El Nino?

14. In the Southern Oscillation, winds across the tropical Pacific reverse direction and blow from west to east—the trade winds weaken or reverse. In a sense, the Southern Oscillation causes El Niño.

Why do Peruvian fisheries decline-often dramatically-in El Nino years?

15. Upwelling within the nutrient-laden Peru Current is responsible for the great biological productivity of the ocean off the coasts of Peru and Chile. Although upwelling may continue during an ENSO event, the source of the upwelled water is nutrient-depleted water in the thickened surface layer approaching from the west (Figure 9.20). When the Peru Current slows and its upwelled water lacks nutrients, fish and seabirds dependent on the abundant life it contains die or migrate elsewhere.

Of the great current circuits in the world ocean, there are ________ in the Northern Hemisphere and ________ in the Southern.

2; 4

Wind driven surface currents are able to mix the upper ___ Meters of the oceans surface

400 Meters

Surface currents extend to what depth in the ocean?

400 meters (1,300 feet)

During a major ENSO event water temperature can rise as much as _____ degrees Celsius.

7

How is La Nina different from El Nino?

After an ENSO event normal circulation sometimes returns with surprising vigor, producing strong currents, powerful upwelling, and chilly and stormy conditions along the South American coast. These contrasting colder-than-normal events are given a contrasting name: La Niña.

The most important current for promoting water exchange among all three oceans is the

Antarctic Circumpolar Current

Why is the antarctic circumpolar current not considered a gyre?

Because is does not flow around the periphery of an ocean basin

How can chlorofluorocarbons (CFCs) be used as such tracers? Would CFC-based methods be equally suitable for analysis of surface currents and thermohaline circulations>

Because they dissolve easily in seawater, chlorofluorocarbons (CFCs) can be used as current tracers. A totally artificial chemical first produced in the 1930s for use as refrigerants, aerosol propellants, and blowing agents for foam, CFCs spread through the ocean like a dye, following oceanic circulation. The speed of thermohaline currents has been measured by careful analysis of their CFC content.

What is meant by "westward intensification"?

Due to the Coriolis effect—which increases as water moves farther from the equator—eastward-moving water on the north side of a gyre is turned sooner and more strongly toward the equator than westward-flowing water at the equator is turned toward the pole. So the peak of the hill described in Figure 9.7 is not in the center of the ocean basin, but closer to its western edge. Its slope is steeper on the western side. If an equal volume of water flows around the gyre, this means the current on the eastern boundary is spread out and slow, and the current on the western boundary is concentrated and rapid - "intensified."

Surface currents affect about 90% of the world's ocean water. True or False?

False

Surface or wind-driven currents move water primarily in a vertical direction in the ocean. True or False?

False

The vertical movement of water due to changes in temperature and salinity is called Ekman transport. True or False

False

How does wind blowing over a surface current influence the climate downward?

If a continent is downwind of a mass of warm water, the atmosphere will transfer some of the heat to the continent. For example, the mild climates of Edinburgh, Dublin, and London are due to eastward-moving air only recently in contact with the relatively warm North Atlantic Current.

Why are western boundary currents so fast and deep?

If an equal volume of water flows around the gyre, this means the current on the eastern boundary is spread out and slow, and the current on the western boundary is concentrated and rapid - "intensified."

What two general methods are used to study ocean currents?

Methods of measuring currents divide into the float method and the flow method.

What is caballing?

Mixing of two water masses of identical densities but different temperatures and salinities, such that the resulting mixture is denser than its components.

Traditional methods of studying currents are being replaced with high-tech devices. How do some of these work?

Modern research on currents is being carried out by devices that measure current speed by sensing the electromagnetic force generated by seawater as it moves in Earth's magnetic field, Doppler current profilers that project beams of sonic pulses ("pings") into the water each second, autonomous gliders like the Slocums, and other promising technologies.

When pressure differences in the western and eastern Pacific cause the trade winds to reverse it is called:

Southern Oscillation

Compare the length of time required for completion of a circuit of surface circulation to that needed for thermohaline circulation.

The circulation time of most deep water about 200 to 300 years. In contrast, a bit of surface water in the North Atlantic gyre may take only a little more than a year to complete a circuit.

How can wind-driven horizontal movement of water induce vertical movement in surface water?

The friction of wind blowing from the north along the ocean surface causes the water next to the west coast of a continent to begin moving. Coriolis effect deflects the water to the right (in the Northern Hemisphere), and the resultant Ekman transport moves it offshore. Deep water then rises (moves vertically) to replace the seaward-moving surface water.

How many large gyres exist in the world ocean?

There are six major gyres in the world ocean

Where do cold-core eddies form?

They form in the gulf stream as it flows eastward upon leaving the coast of NA off Cape Hatteras

In the Northern Hemisphere, the water surface of the open ocean moves 45° to the right of the wind. True or False

True

The densest water in the world is formed in the Antarctic. True or False

True

The main current in Antarctic waters is the Antarctic Circumpolar Current, also called the West Wind Drift. True Or False?

True

The name of the current that flows from north to south along the west coast of North America is the California current. True or False

True

The circulation of water at great depths is driven by: a. density. b. surface winds. c. salinity only. d. temperature only.

a. density.

What is the relationship between surface currents and the climate of adjacent continents?

Warm water flows to higher latitudes, transfers heat to the air and cools, moves back to low latitudes, absorbs heat again, and the cycle repeats. The greatest amount of heat transfer occurs at mid-latitudes, where about 10 million billion calories of heat are transferred each second. Some of this warmth is transferred to adjacent continents

Why does seawater in most surface currents flow around the periphery of ocean basins?

Water flow in a gyre is dynamically balanced between the downhill urge of the pressure gradient and the uphill tendency of Coriolis deflection

What happens in convergence zones? How is caballing associated with convergence zones?

Water masses butt against one another in convergence zones. In some cases, two distinct water masses with the same density but with different temperatures and salinities will combine at a convergence to produce a new water mass of greater density. This mixing-and-sinking process is called caballing.

What drives the Antarctic circumpolar current?

Westerly winds

Narrow, fast, and deep currents that move water polar-ward are called

Western boundary currents

What differs between western boundary currents and eastern boundary currents?

Western boundary currents tend to be hot, fast, and deep. Eastern boundary currents are cold, slow, and shallow.

How do eddies form?

When western boundary currents connect to eddies that trap cold or warm water in their centers and then separate from the main flow

How is up welling linked to biological productivity?

While nutrients in surface water are sometimes depleted by the rapid growth of organisms, deep water is often rich in nutrients. When that water rises toward the sunlit surface, biological productivity increases.

How are hills in the middle of the ocean maintained?

Wind Energy

The surface ocean gyres: a. have the strongest currents on their eastern sides. b. are primarily the result of wind patterns. c. have water moving in the same direction from the sea surface to the bottom. d. are confined on all sides by the continents

b. are primarily the result of wind patterns.

Western boundary currents: a. carry cool polar water toward the equator. b. transport water in a diffuse, ill defined stream. c. transport enormous volumes of water. d. are relatively shallow, broad and slow.

c. transport enormous volumes of water.

Antarctic bottom water is noted for its extreme...?

density

In the Northern Hemisphere, surface currents flow to the ________ of wind direction; in the Southern Hemisphere, surface currents flow to the ________.

right; left