Posted: April 18th, 2022

Discuss the factors that create and influence ocean currents.

The Restless Ocean

Chapter 10 Lecture

Natalie Bursztyn

Utah State University

Foundations of Earth Science

Eighth Edition

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Discuss the factors that create and influence ocean currents.

Describe the influence ocean currents have on climate.

Focus Questions 10.1

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Ocean currents

Masses of water that flow from one place to another

Surface currents develop from friction between wind and the ocean surface

Huge, slowly moving gyres

The Pattern of Ocean Currents

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Five main gyres

North Pacific gyre

South Pacific gyre

North Atlantic gyre

South Atlantic gyre

Indian Ocean gyre

Related to atmospheric circulation

The Pattern of Ocean Currents

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The Pattern of Ocean Currents

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Coriolis effect

Result of the Earth’s rotation

Deflects surface currents

To the right in the Northern Hemisphere

To the left in the Southern Hemisphere

Four main currents generally exist within each gyre

The Pattern of Ocean Currents

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Importance of surface currents on climate

Warm currents transfer heat from low latitudes into higher latitudes (moderating effect)

Influence of cold currents is most pronounced in the tropics or during summer months in the middle latitudes

Chill the air

Increase aridity

Ocean Currents Influence Climate

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Ocean Currents Influence Climate

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Ocean Currents Influence Climate

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Explain the processes that produce coastal upwelling the ocean’s deep circulation.

Focus Question 10.2

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Coastal upwelling

The rising of cold deep water to replace warm surface water

Wind-induced vertical movement

Most characteristic along west coasts

Coastal winds combined with Coriolis effect cause water to move away from shore

Upwelling and Deep-Ocean Circulation

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Coastal Upwelling

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Deep-ocean circulation

A response to density differences

Factors creating a dense mass of water

Temperature (cold water is dense)

Salinity (density increases with increasing salinity)

Called thermohaline circulation

Deep-Ocean Circulation

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Most water in deep-ocean currents begins in high latitudes at the surface

A simple model of ocean circulation is a conveyor belt traveling from the Atlantic Ocean, through the Indian and Pacific Oceans, and back again

Deep-Ocean Circulation

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Deep-Ocean Circulation

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Explain why the shoreline is considered a dynamic interface.

List the factors that influence the height, length, and period of a wave.

Describe the motion of water within a wave.

Focus Questions 10.3

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Continental and oceanic processes converge along coasts

Landscapes undergoing rapid change

Interface (common boundary where different parts of a system interact) between continent, ocean, and atmosphere

Transition zones between marine and continental depositional environments

The Shoreline: A Dynamic Interface

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Shorelines are constantly being modified by:

Waves and storms

Sea level change

Stream erosion and deposition

Glaciation

Volcanic activity

Tectonic forces

Human activity

A Dynamic Interface

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A Dynamic Interface

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Waves

Energy traveling along the interface between ocean and atmosphere

Derive energy and motion from wind

Ocean Waves

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Wave height

Vertical distance between a trough and a crest

Wavelength

Horizontal distance between successive crests (or troughs)

Wave period

Time interval for one full wave to pass a fixed position

Wave Characteristics

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Wave height, length, and period depend on:

Wind speed

Length of time the wind blows

Fetch (distance the wind travels)

As the wave travels, the water passes energy in a circular orbital motion.

Wave Characteristics

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Circular Orbital Motion

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Waves in the Surf Zone

Waves are unaffected by depth until they approach shore

Waves begin to “feel bottom” at water depth equal to wave base

Slightly faster waves farther out to sea catch up and decrease the wavelength, which causes the wave to grow steadily higher

When the wave is too steep to support itself, the wave front collapses, or breaks

Surf is turbulent water created by breaking waves

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Ocean Waves

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Describe how waves erode and move sediment along the shore.

Focus Question 10.4

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Beaches are composed of whatever material is available

Some have a significant biological component

Material does not stay in one place

Beaches and Shoreline Processes

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Beaches and Shoreline Processes

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Wave erosion

Caused by wave impact and pressure

Breaks down rock, supplying sand to beaches

Abrasion is the sawing and grinding action of water armed with rock fragments

Wave Erosion

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Wave Erosion

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Rivers of sand

Sand in the surf zone moves roughly parallel to the shoreline

Wave energy causes sand to move perpendicular to the shoreline

Wave refraction

Bending of waves

As waves first touch bottom in the shallows they are slowed, causing them to bend

Wave arrives parallel to shore

Sand Movement on the Beach

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Wave refraction

Wave energy is concentrated against the sides and ends of the headland

Wave erosion straightens an irregular shoreline

Sand Movement on the Beach

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Sand Movement on the Beach

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Longshore transport

Beach drift

Sediment moves in a zigzag pattern along the beach face

Longshore current

Current in surf zone

Parallel to shore

Moves substantially more sediment than beach drift

Sand Movement on the Beach

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Beaches and Shoreline Processes

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Describe the features typically created by wave erosion and those resulting from sediment deposited by longshore transport processes.

Focus Question 10.5

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Shoreline erosion influenced by local factors:

Proximity to sediment-laden rivers

Degree of tectonic activity

Topography and composition of the land

Prevailing wind and weather patterns

Configuration of the coastline

Shoreline Features

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Wave-cut cliff

Wave-cut platform

Marine terraces

Associated with headlands

Sea arch

Sea stack

Erosional Features

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Erosional Features

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Erosional Features

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Spit

A ridge of sand extending from the land into a bay with a hooked end

Baymouth bar

A sand bar that completely crosses a bay

Tombolo

A ridge of sand that connects an island to the mainland or another island

Depositional Features

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Depositional Features

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Barrier islands

Mainly along the Atlantic and Gulf Coasts

Parallel the coast

Originate in several ways:

As spits severed from the mainland

Created when turbulent waters heaped up sand scoured from the bottom

Former sand-dune ridges that originated along the shore during the last glacial period

Depositional Features

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Depositional Features

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The Evolving Shore

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Distinguish between emergent and submergent coasts.

Contrast the erosion problems faced along different parts of America’s coast.

Focus Questions 10.6

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Erosion problems along U.S. Coasts

Shoreline erosion problems are different along the opposite coasts

Contrasting America’s Coasts

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Shoreline classification is based on changes with respect to sea level

Emergent coast

Uplift of the land, or

A drop in sea level

Coastal Classification

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Submergent coast

Land adjacent to sea subsides, or

Sea level rises

Features of a submergent coast

Highly irregular shoreline

Estuaries

Drowned river mouths

Coastal Classification

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Coastal Classification

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Erosion problems along U.S. Coasts

Atlantic and Gulf Coasts

Development occurs mainly on barrier islands

Face open ocean

Receive full force of storms

Development taken place more rapidly than understanding barrier island dynamics

Atlantic and Gulf Coasts

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Atlantic and Gulf Coasts

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Erosion problems along U.S. Coasts

Pacific Coast

Characterized by relatively narrow beaches backed by steep cliffs and mountain ranges

Major problem is the narrowing of the beaches

Sediment for beaches is interrupted by dams and reservoirs

Rapid erosion occurs along the beaches

Pacific Coast

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Pacific Coast

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Summarize the ways in which people deal with shoreline erosion problems.

Focus Question 10.7

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Responses to erosion problems

Hard stabilization—Building structures

Groins

Barriers built at a right angle to the beach

Designed to trap sand

Breakwaters

Barriers built offshore and parallel

Protect boats from breaking waves

Stabilizing the Shore

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Hard Stabilization

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Seawalls

Armors the coast against breaking waves

Often not effective

Hard Stabilization

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Beach nourishment by adding sand to the beach system

Relocating buildings away from beach

Alternatives to Hard Stabilization

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Explain the cause of tides as well as their monthly cycles and other patterns.

Describe the horizontal flow of water that accompanies the rise and fall of the tides.

Focus Questions 10.8

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Changes in elevation of ocean surface

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

Tides

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Tides

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Spring tide

During new and full moons

Gravitational forces added together

Larger tidal troughs and tidal bulges

Large daily tidal range

Monthly Tidal Cycle

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Neap tide

First and third quarters of the Moon

Gravitational forces are offset

Daily tidal range is least

Monthly Tidal Cycle

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Many factors influence the tides:

Shape of the coastline

Configuration of the ocean basin

Water depth

Diurnal pattern

Semidiurnal pattern

Mixed pattern

Tidal Patterns

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Diurnal tidal pattern

A single high and low tide each tidal day

Occurs along northern shore of Gulf of Mexico

Semidiurnal tidal pattern

Two high and low tides each tidal day

Little difference in high and low water heights

Mixed tidal pattern

Two high and two low waters each day

Large inequality in high water heights, low water heights, or both

Prevalent along the Pacific Coast of the United States

Tidal Patterns

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Tidal Patterns

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Horizontal flow accompanying the rise and fall of tides

Flood current

Advances into the coastal zone

Ebb current

Seaward moving water

Tidal flats are alternatively covered and uncovered by tides

Sometimes tidal deltas are created

Tidal Currents

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Tidal Currents

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