OCN- Chapter 5 Review

unstable system

"An system that does not return to its original state or condition following a disturbance."

deep layer

"Beneath the pycnocline, this dark, cold zone accounts for most of the ocean's mass."

water mass

" Large, homogeneous volume of water, exhibiting characteristic ranges of temperature and salinity."

mixed layer

" The surface of the ocean water to which sunlight penetrates and surface winds mix well to uniform density, ranging from 25-200 m (82-655 ft.)"

neutrally stable system

"A system that neither departs from its new state nor returns to its previous state following a disturbance, such as when layered water is mixed so the density it now uniform."

stable system

"A system that returns to its initial state or condition following a disturbance. "

pycnocline

"Between the mixed layer and the deep layer where water density increases rapidly with depth because of changes in temperature and/or salinity; typically extends to depth of 500-1000 m (1600-3300 ft.)"

subtropical gyres

"Centered near 30° N latitude in the North and South Atlantic and Pacific Oceans and 30° S latitude in the Indian Ocean, gyres that rotate in the same direction as the prevailing atmospheric subtropical anticyclone, which is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere."

equatorial upwelling

"Due to the Coriolis Effect, the west-ward flowing, wind-driven surface currents turn northward on the north side of the equator and southward on the south side, so surface waters flow away from the equator, producing upwelling."

subpolar gyres

"Found at high latitudes of the Northern Hemisphere, such as the Alaska gyre in the far North Pacific and the gyre south of Greenland in the far North Atlantic, these gyres are smaller than subtropical gyres and driven by counterclockwise surface winds in the Aleutian and Icelandic subpolar low pressure systems."

coastal upwelling

"In the Northern Hemisphere, when a prevailing wind blows from the north along a fairly straight stretch of coastline on the western side of the continent, water is deflected to the right by Ekman transport and surface water flows away from the coast, producing upwelling. In the Southern Hemisphere, wind from the south results in upwelling along the coast."

coastal downwelling

"In the Northern Hemisphere, when a prevailing wind from the south blows along a west coast, water is deflected to the right by Ekman transport to the right and surface water flows toward the coast, producing downwelling. In the Southern Hemisphere, wind from the north results in downwelling along the coast."

rings

"Large turbulent rotating warm-core and cold-core eddies spawned by western boundary currents."

meridional overturning circulation (MOC)

"Large-scale overturning in the meridional (north-south) plane of the ocean that transports heat, salinity, and carbon dioxide throughout the global ocean."

gyres

"Large-scale roughly circular surface current systems in the ocean basins sustained by geostrophic flow."

eastern boundary currents

"Produced by subtropical ocean gyre along the eastern portion of the ocean, the current is slow (1 km per hr or 0.6 mph), wide and shallow, and not close to the coast."

western boundary currents

"Produced by subtropical ocean gyre along the western portion of the ocean, the current is swift (averaging 3-4 km per hr or 1.8-2.5 mph), deep and narrow (no more than 50-75 km or 30-47 mi. across), and constrained against the edge of the continental shelf. "

doldrums

"Region named by mariners that is generally north of the equator, which shifts farthest north during the Northern Hemisphere summer and farthest south during Northern Hemisphere winter and produces light and variable winds where warm and humid air ascends in the intertropical convergence zone."

warm-core rings

"Rings formed from the north side of the Gulf Stream, typically 100-200 km (60-120 mi.) across, enclosing warm waters extending to depths of 1500 m (4900 ft.), and rotating clockwise when viewed from above; sometimes transport tropical animals to coastal waters."

cold-core rings

"Rings formed from the south side of the Gulf Stream, about 300 km (185 mi.), enclosing cold water to depths past 4000 m (13,000 ft.), and rotating counterclockwise when viewed from above; often carry nutrients and organisms into Sargasso Sea."

brine rejection

"Salt in the water is excluded from ice crystals when sea ice forms, creating salter, high density water."

eddies

"Slow swirling motions in the ocean that break off away from gyres or currents and are affected by the Coriolis Effect"

thermohaline circulation

"The density driven movement of water with depth in the ocean; ocean water density increases with decreasing temperature and increasing salinity."

Ekman spiral

"The model of a steady wind blowing across the ocean that causes water at increasing depth to move at an angle of 45° to the right of the wind in the Northern Hemisphere and 45° to the left of the wind in the Southern Hemisphere; which drags the water below it further in the same direction, but at a slower rate, until at 100-150 m (330-500 ft.) depth, the spiral completes about half a turn"

Ekman transport

"The net movement in the Ekman spiral: 90° to the right of the prevailing wind direction in Northern Hemisphere and 90° to the left of the prevailing wind direction in the Southern Hemisphere."

open ocean convection

"When cold winds cool the surface water until its density is greater than that of the water below until the more dense water sinks and less dense, warmer water ascends."

thermocline

"When the pycnocline's declining temperature is responsible for the increase in density with depth."

halocline

"When the pycnocline's increase in salinity is responsible for the increase in density with depth"

geostrophic flow

A current in the atmosphere in which the Coriolis force and the pressure gradient are in balance.

Describe the halocline, thermocline, and pycnocline structures in the ocean.

A halocline marks a layer of ocean water in which the salinity changes rapidly with depth compared to salinity changes in layers of water above and below. Similarly, a thermocline marks a layer in which the temperature changes rapidly with depth relative to temperature changes above and below. Finally, a pycnocline delineates a layer of ocean water in which there is a rapid increase in water density with depth compared to density changes above and below due to changes in salinity, temperature, or both in the water column.

Define a water mass. How are water masses classified?

A water mass is a large, homogeneous volume of water with limited characteristic ranges of temperature and salinity. Water masses are classified based on their source region and the relative depth in the ocean where they reach density equilibrium with surrounding waters.

Describe the role played by Ekman transport in coastal upwelling. Distinguish between coastal upwelling and equatorial upwelling.

Coastal upwelling occurs where Ekman transport moves surface water away from the coast. For example, winds flowing toward the south produce upwelling along the California coast. The prevailing trade winds converge toward the equator. Ekman transport causes surface waters in equatorial waters to flow away from the equator, that is, toward the northwest in the Northern Hemisphere and toward the southwest in the Southern Hemisphere. The consequence is equatorial upwelling.

In the Northern Hemisphere, how does the direction of Ekman transport of ocean water compare to the surface wind direction?

Ekman transport of ocean water is at 90° to the right of the surface wind direction in the Northern Hemisphere.

Compare the rotation direction and productivity in warm- and cold-core rings of the Northern Hemisphere. Do cold-core rings associated with the Gulf Stream entrain waters from coastal areas or the Sargasso Sea?

In the Northern Hemisphere, warm-core rings rotate clockwise as seen from above and cold-core rings rotate counterclockwise. Cold-core rings associated with the Gulf Stream entrain waters from coastal areas and have higher productivity.

Compare and Contrast the surface ocean currents on the eastern and western sides of the subtropical gyres.

Surface currents flow poleward on the western side of subtropical gyres and equatorward on the eastern side. Surface currents on the western sides of these gyres (western boundary currents) are faster, deeper, and narrower than their eastern counterparts.

Describe the significance of the meridional overturning circulation (MOC) in Earth's climate system.

The meridional overturning circulation (MOC) begins with the formation and subsequent sinking of cold, salty water at high latitudes (Norwegian and Labrador Seas in the North Atlantic and near Antarctica). This relatively dense bottom water flows equatorward and eventually warms and rises to the surface. The resulting north-south transport of heat energy, salt, and carbon dioxide plays an important role in Earth's climate system.

How does the speed of water motion in the thermohaline circulation compare to that of wind-driven surface ocean currents?

The ocean's thermohaline circulation is generally much slower than surface ocean currents.

How does water density vary with depth in the ocean?

Water density primarily changes due to changes in temperature and salinity. As the density increases, water sinks and flows to the depth at which the surrounding water has the same density (or reaches the sea floor). Differences in water density drive the deep water circulation.

Distinguish between the directions of the trade winds in the Northern Hemisphere versus those in the Southern Hemisphere. What is the significance of the intertropical convergence zone?

Trade winds blow from the northeast (toward the southwest) in the Northern Hemisphere and from the southeast (toward the northwest) in the Southern Hemisphere. The trade winds converge in the intertropical convergence zone (ITCZ), a discontinuous belt of low air pressure with thunderstorms paralleling the equator.