Dynamic OceanOceanography Part 3

Ocean Currents

Ocean Currents masses of ocean water that flow

from one place to another develop from friction between the

ocean and the wind that blows across its surface

Factors affecting surface current patterns:

pattern of global windsdistribution of major landmassesGravityFrictionCoriolis effect

Pattern of Ocean Currents

Gyres = huge, circular-moving current systems; large whirls of water within an ocean basin

North Pacific Gyre

South Pacific Gyre

North Atlantic Gyre

South Atlantic

Gyre Indian OceanGyre

5 Main Gyres

1. North Pacific Gyre – clockwise2. South Pacific Gyre -

counterclockwise3. North Atlantic Gyre - clockwise4. South Atlantic Gyre -

counterclockwise5. Indian Ocean Gyre -

counterclockwise

Average Surface Ocean Currents in February–March

When the winds change direction, the surface currents

also reverse direction.

North Pacific Gyre

4 Major Currents1. North Equatorial Current2. Kuroshio Current3. North Pacific Current4. California Current

South Pacific Gyre

4 Main Currents1. South Equatorial Current2. East Australian Current3. West Wind Drift4. Peru Current

North Atlantic Gyre

4 Major Currents1. North Equatorial Current2. Gulf Stream Current3. North Atlantic Current4. Canary Current

South Atlantic Gyre

4 Main Currents1. South Equatorial Current2. Brazil Current3. West Wind Drift4. Benguela Current

Indian Ocean Gyre

4 Main Currents1. South Equatorial Current2. Agulhas Current3. West Wind Drift4. West Australian Current

Anyone who navigates the oceans need to be aware of the currents.

Voyage time can be reduced by traveling with the current

Ocean Currents Influence Climate

When currents from low-latitude regions move to higher latitudes, they transfer heat from warmer to cooler areas on Earth.

Ex: the North Atlantic Current—an extension of the warm Gulf Stream—keeps Great Britain and much of northwestern Europe warmer during the winter than one would expect for their latitudes, which are similar to the latitudes of Alaska and Labrador

Ocean Currents Influence Climate

The prevailing westerly winds carry the moderating effects far inland.

Ex: Berlin, Germany (52 degrees north latitude), has an average January temperature similar to that experienced at New York City, which lies 12 degrees latitude farther south

Ocean CurrentsInfluence Climate Cold currents originating

in cold high-latitude regions tend to moderate the warm temperatures of adjacent land areas. Ex: the cool Benguela Current off the

western coast of southern Africa moderates the tropical heat along this coast. Walvis Bay (23° south latitude), a town adjacent to the Benguela Current, is 5° C (9° F) cooler in summer than Durban, which is 6° latitude farther poleward but on the eastern side of South Africa, away from the influence of the current

Ocean Currents Influence Climate

Ocean currents play a major role in maintaining Earth’s heat balance

Deep Ocean Circulation

This component of ocean circulation is a response to density differences among water masses that cause denser water to sink and slowly spread out beneath the surface

also referred to as thermohaline circulation Recall: An increase in seawater density can be

caused by a decrease in temperature or an increase in salinity.

The Shoreline

Basic Features of the Coastal Zone

Shoreline - the line that marks the contact between land and sea

Shore - the area that extends between the lowest tide level and the highest elevation on land that is affected by storm waves.

Coast - extends inland from the shore as far as ocean-related features can be found.

Coastline - marks the coast’s seaward edge

Coastal Zone

Basic Features of the Coastal Zone

Foreshore - the area exposed when the tide is out (low tide) and submerged when the tide is in (high tide).

Backshore - landward of the high-tide shoreline; It is usually dry, being affected by waves only during storms.

Nearshore Zone - lies between the low-tide shoreline and the line where waves break at low tide.

Offshore Zone - Seaward of the nearshore zone

Coastal Zone

Beaches an accumulation of sediment found along the

landward margin of the ocean or a lake

Berms - relatively flat platforms often composed of sand that are adjacent to coastal dunes or cliffs and marked by a change in slope at the seaward edgeBeach face - the wet sloping surface that extends from the berm to the shoreline

Beaches are composed of whatever material is locally abundant

Waves Ocean waves are energy traveling along the

interface between ocean and atmosphere, often transferring energy from a storm far out at sea over distances of several thousand kilometers

Most ocean waves derive their energy and motion from the wind.

When a breeze is less than 3 kilometers (2 miles) per hour, only wavelets appear.

At greater wind speeds, more stable waves gradually form and advance with the wind.

Wave Characteristics

Wave Characteristics The tops of the waves are the crests, which are

separated by troughs. Water Level – the level that the water would occupy

if there were no waves. Wave Height - the vertical distance between trough

and crest Wavelength - horizontal distance between

successive crests (or troughs) Wave Period - the time it takes one full wave—one

wavelength— to pass a fixed position

Tides daily changes in the elevation of the ocean surface Ocean tides result from the gravitational attraction

exerted upon Earth by the Moon and, to a lesser extent, by the Sun

Causes: The Moon’s gravitational force can cause the water to

bulge on the side of Earth nearer the Moon An equally large tidal bulge is produced on the side of

Earth directly opposite the Moon

Tides Because the position of the

Moon changes only moderately in a single day, the tidal bulges remain in place while Earth rotates “through” them

Most places on Earth experience two high tides and two low tides each day

Tidal bulges exist in fixed positions relative to the Moon

When the Moon is in the full or new position, the tidal bulges created by the Sun and Moon are aligned, there is a large tidal range on Earth, and spring tides are experienced.

When the Moon is in the first- or third-quarter position, the tidal bulges produced by the Moon are at right angles to the bulges created by the Sun. Tidal ranges are smaller, and neap tides are experienced.

Tidal Patterns

3. Mixed tidal pattern - two highs and lows of unequal heights during each tidal day

1. Diurnal - one high and low tide each tidal day2. Semi-diurnal - two highs and lows of approximately equal heights during each tidal day