Oceanography Ch. 7

Mixed Layer

Surface layer tens of meters thick with relatively constant temperature.

Thermocline

Extends from bottom of mixed layer to 1000m deep, temperature drastically changes with depth.

Isothermal

uniform temperature

Halocline

Water layer with large change in salinity with depth

Pynocline

Water layer with large change in pressure with depth.

Thermohaline Circulation

Vertical circulation caused by changes in density, driven by variations in temperature and salinity

Downwelling Zones

Sinking of water, caused by an increase in its density

Convergence

Surface waters driven together by wind, results in downwelling.

Divergence

Surface waters driven away from a center, results in upwelling

Isopycnal

uniform density

Isohaline

uniform salinity

Water Type

Body of water identified by a specific range of temperature and salinity.

Water Mass

Body of water with similar patterns of temperature and salinity from surface to depth.

Ekman Spiral

Wind creates a surface current that spirals in a clockwise direction as depth decreases, flowing in the opposite direction of the wind at about 100m depth. (spiral is in the opposite direction in the southern hemisphere)

Ekman Layer

Surface layer of water that contains the Ekman spiral

Ekman Transport

Net movement of water in right angle directions to the wind.

Gyre

Circular movement of water. (larger scale than eddies)

Geostrophic Flow

Horizontal flow of water when there is a balance between gravitational forces and the coriolis effect.

Western Intesification

Increase in speed of geostrophic currents as they move along the western boundary of an ocean basin.

Eddies

Pockets of water moving in a circular motion.

Langmuir Cells

Shallow wind-driven circulation.

Arctic and Antarctic Convegence

Permanent zone of convergence at about 50°N and S

Drift Bottle

Bottle released at sea used to study currents.

Current Meter

Instrument that measures speed and direction of a current.

How does temperature generally vary with depth?

It decreases

What is a mixed layer?

A Surface layer tens of meters thick with relatively constant temperature.

What is the thermocline?

Layer that extends from bottom of mixed layer to 1000m deep, temperature drastically changes with depth.

What does Isothermal mean?

uniform temperature

What is a halocine?

A Water layer with large change in salinity with depth.

What is the relationship between density and temperature? Between density and salinity?

As temperature decreases, density increases (until it begins to freeze); as salinity increases density increases.

What is thermocline circulation?

Vertical circulation caused by changes in density, driven by variations in temperature and salinity

What is upwelling?

Rising of water, caused by a decrease in density

What is downwelling?

Sinking of water, caused by an increase in its density.

What is surface convergence?

Surface waters driven together by wind, results in downwelling.

What is surface divergence?

Surface waters driven away from a center, results in upwelling.

What does isopycnal mean?

uniform density

What does isohaline mean?

uniform salinity

What is a water type?

A Body of water identified by a specific range of temperature and salinity.

What is a water mass?

A Body of water with similar patterns of temperature and salinity from surface to depth

Explain how water types with different temperature and salinity can have the same density?

Warm water with a higher salt content can have the same density as cooler water and lower salinity

What is the Ekman spiral and Ekman transport?

Ekman spiral: Wind creates a surface current that spirals in a clockwise direction as depth decreases, flowing in the opposite direction of the wind at about 100m depth. (spiral is in the opposite direction in the southern hemisphere)

Ekman transport: Net movement of water in right angle directions to the wind

What is an ocean gyre? How does it form?

A Circular movement of water. (larger scale than eddies) Trade winds causes water current from east to west on either side of the equator, then deflected away from the equator until the westerlies move the current from the west back to the east and are then deflected toward the equator.

What and where are the 5 major ocean gyres?

Indian ocean gyre, north and south Pacific gyres, north and south Atlantic gyres.

What is Geostropic flow

Horizontal flow of water when there is a balance between gravity and the coriolis effect

Name the currents that make up each of the five major ocean gyres. Which ones are the western boundary currents and which ones are the eastern boundary currents?

Indian ocean gyre (counterclockwise): South equatorial current, Agulhas current (western boundary), West Australia current (eastern boundary)

North Pacific ocean gyre (clockwise): North equatorial current, North Pacific current, Kuroshio current (western boundary), California current (eastern boundary)

South Pacific ocean gyre (counterclockwise): South equatorial current, East Australian current (western boundary), Peru current (eastern boundary)

North Atlantic ocean gyre (clockwise): North equatorial current, North Atlantic current, Gulf stream (western boundary) Canary current (eastern boundary)

South Atlantic ocean gyre (counterclockwise): South equatorial current, Brazil current (western boundary) Benguela current (eastern boundary)

How does the Equatorial countercurrent form?

Trade winds push the equatorial currents to the west accumulating water on the west side of the basin, within the doldrums where winds are calm or absent, the water flows downslope toward the east.

How does the Antarctic Circumpolar Current flow all the way around Antarctica?

There is no land in its pathway

How fast do ocean surface currents move relative to the wind that generates them?

about 1/100

What unit of measurement is used for current volume transport? What is its value in cubic meters?

The Sverdrup (Sv) equal to about 1 million cubic meters per second

What is Western Intensification and why does it happen?

An increase in speed of geostrophic currents as they move along the western boundary of an ocean basin. This is because the slope of the water is steeper on the western side.

How does changing the width of a current affect its speed?

Narrow currents move faster than wide currents. Same amount of water flow, just forced through a smaller area.

What is an Eddie? How does it form?

A Pocket of water moving in a circular motion. (smaller scale than gyre) when fast moving currents run into slower currents they displace the slower water and begin to spin

What are Langmuir cells? How do they form?

Shallow wind-driven circulation. They are formed by convergence zones that create helixes of moving water along the convergence line.

What is surface divergence? Convergence?

Convergence: Surface waters driven together by wind, results in downwelling.

Divergence: Surface waters driven away from a center, results in upwelling

What are the 5 major zones of convergence?

The tropical convergence at the equator, the two subtropical convergences at about 30°-40°N and S, and The Arctic and Antarctic convergences at about 50°N and S

Where are the three major zones of divergence?

the two tropical divergences and the Antarctic divergence

How can Ekman transport generate coastal upwelling? Downwelling?

The water moves at 90° angles to the wind so when it blows parallel to the coast it will actually drive water away (causing upwelling) or toward the coast (causing downwelling)

What is the Great Ocean Conveyor Belt? How does it form? What path does it take?

It represents the overall effect of the mass movement of warm and cold water on the vertical circulation in the ocean. The formation and sinking of dense water at polar latitudes is considered to start it. Roughly follows gyres at surface, beneath generally from the poles where it is formed to the equator

Describe the Pacific

Describe the Pacific Decadal Oscillation and its causes.

North-south current shift, associated with changes in atmospheric pressure and climate shifts.

Describe the North Atlantic Oscillation. What effect does it have on Europe's climate?

A pool of cold water circulating around the northern Atlantic. Harsh winters.

What measurements are necessary to define a current

speed and direction

Name at least 3 methods to measure ocean currents? How do they work?

Buoys: drift with the current and signal their position

Current meter: stationary, they measure speed and direction as water moves past.

Drift bottle: bottle released to float along current

What is the Doppler effect?

A change in the observed frequency of a sound wave caused by currents flowing toward or away from the observation point. (noise difference when an ambulance goes past you)