The Dynamic Ocean

The Dynamic Ocean

• Surface Circulation• Deep-Ocean Circulation• Shorelines & Shoreline Features• Waves & Wave Erosion• U.S. Coastal Problems• Tides

Terms• Gyre

– A circular pattern of connected surface currents

• Tides– Daily rise and fall of shorelines around the

world ocean

• Tidal range– Difference in height between high and low tide

Surface Circulation

PSCI 131: The Dynamic Ocean

Surface CirculationPSCI 131: The Dynamic Ocean

• Surface ocean currents are “rivers” with very different temperature and density than surrounding water

• Driven by wind blowing across ocean surface

• Ultimate energy source: Sun

• Carry warm water from tropics to poles and vice versa

Surface Current PatternsPSCI 131: The Dynamic Ocean: Surface Circulation

Influence on Climate: The Gulf StreamPSCI 131: The Dynamic Ocean: Surface Circulation

• Moves warm water north from tropics

• Gives British Isles a temperate climate

North America

Water movement

UpwellingPSCI 131: The Dynamic Ocean: Surface Circulation

• Vertical movement of water

• Deeper water moves up to replace surface water moved away by winds

• Depths: 150-1,000 feet

• Replenishes nutrients

UpwellingPSCI 131: The Dynamic Ocean: Surface Circulation

• Upwelling along African coast

Deep-Ocean Circulation

PSCI 131: The Dynamic Ocean

Deep-Ocean CirculationPSCI 131: The Dynamic Ocean

• Much deeper than surface circulation or upwelling – can affect ocean floor

• Vertical motion driven by density differences– If upper layers become denser, they sink

• Density controlled by temperature and salinity– aka “thermohaline” circulation

Deep-Ocean CirculationPSCI 131: The Dynamic Ocean

Cold, dense surface water in polar regions sinks, driving deep-ocean circulation

Shorelines & Shoreline Features

PSCI 131: The Dynamic Ocean

Shoreline: TerminologyPSCI 131: The Dynamic Ocean: Shorelines

• Shoreline: contact between water and land• Coast: area from shoreline inland as far as

ocean-related features are found• Coastline

Shoreline: TerminologyPSCI 131: The Dynamic Ocean: Shorelines

• Coastline: Highest line affected by storm waves

PSCI 131: The Dynamic Ocean: Shorelines: Terminology

• Shore: low tide line to coastline– Foreshore: low tide line to high tide line– Backshore: high tide line to coastline

PSCI 131: The Dynamic Ocean: Shorelines: Terminology

• Nearshore: surf line to low tide line

• Offshore: beyond surf line

Shoreline Features: BeachesPSCI 131: The Dynamic Ocean: Shorelines

• Accumulations of sediment along margin of ocean or lake

• Berm: level area, usually dry• Beach face: sloping area, usually wet• Berm:

Shoreline Features: BeachesPSCI 131: The Dynamic Ocean: Shorelines

• Composition: any locally available sediment type– Quartz sand– Shells– Volcanic material– Etc.

Black volcanic sand

Shells

Rocky Great Lakes beach

Shoreline Features: Barrier islands

PSCI 131: The Dynamic Ocean: Shorelines

Wave-cut cliff

(uplifted wave-cut platform)

• Wide beaches – Separated from mainland by

marshes or narrow seaways

• Shaped by wave erosion and storms

Shoreline Features: Cliffs, Platforms, Terraces

PSCI 131: The Dynamic Ocean: Shorelines

Wave-cut cliff

(uplifted wave-cut platform)

Shoreline Features: Sea Arches and Sea Stacks

PSCI 131: The Dynamic Ocean: Shorelines

Shoreline Features: Spits, Bars, Tombolos

PSCI 131: The Dynamic Ocean: Shorelines

Changing Shoreline Features Along Irregular Coastlines

PSCI 131: The Dynamic Ocean: Shorelines

Changing Shoreline Features Along Irregular Coastlines

PSCI 131: The Dynamic Ocean: Shorelines

Evolving Shoreline Features Along Irregular Coastlines

PSCI 131: The Dynamic Ocean: Shorelines

Waves and Wave Erosion

PSCI 131: The Dynamic Ocean

Ocean WavesPSCI 131: The Dynamic Ocean: Waves & Wave Erosion

• Created by wind

• Energy propagating along water-air boundary

• Waves move differently in deep and shallow ocean– Deep: no net movement of water, circular motion– Shallow: water is displaced, linear motion

Ocean WavesPSCI 131: The Dynamic Ocean: Waves & Wave Erosion

Wave base

Wave base: depth below which water does not “feel” waveWave base = ½ wavelength

Deep ocean wave motion is circularPSCI 131: The Dynamic Ocean: Waves & Wave Erosion

Boat returns to starting position

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Shallow ocean wave movementPSCI 131: The Dynamic Ocean: Waves & Wave Erosion

Wave base

Wave ErosionPSCI 131: The Dynamic Ocean: Waves & Wave Erosion

• Direct impact of water• Abrasion by sediment in the water

Cliff undercut by wave impactsRocks polished by abrasion

Shoreline Sediment MovementPSCI 131: The Dynamic Ocean: Waves & Wave Erosion

• Longshore transport

– Beach drift

– Longshore currents

U.S. Coastal Problems

PSCI 131: The Dynamic Ocean

Pacific CoastPSCI 131: The Dynamic Ocean: U.S. Coastal Problems

• Emergent: Steep, geologically active, rugged– Cliffs with narrow beaches

• Beaches are getting narrower– Natural sand supplies from rivers

have been restricted by damming

• Since beaches absorb wave energy, narrower beaches means faster wave erosion of cliffs

Atlantic and Gulf CoastsPSCI 131: The Dynamic Ocean: U.S. Coastal Problems

• Submergent: Flat, geologically quiet– Wide beaches, barrier islands

• Rising sea level is causing more frequent flooding– Gentle slope of coastline

amplifies effect of sea level rise

• Wetlands and barrier islands– Natural protection for

mainland from storms– Draining and development is

diminishing this protectionGulf Coast wetlands

Tides

PSCI 131: The Dynamic Ocean

PSCI 131: The Dynamic Ocean: Tides

Moon’s gravity pulls harder on side closer to Moon, creating bulges of ocean water on opposite sides of Earth

Tidal bulge animation

Bulges are always aligned with Moon, and Earth rotates through them

Tides are caused by Moon’s gravity (and Sun’s to a lesser extent)

PSCI 131: The Dynamic Ocean: Tides

Monthly Tidal Cycle

Spring tide: Lunar and solar gravity work together to produce largest tidal range twice per month

PSCI 131: The Dynamic Ocean: Tides

Monthly Tidal Cycle

Neap tide: Lunar and solar gravity work against each other to produce smallest tidal ranges twice per month

End of Chapter