The Oceans Waves Steve TerrillStock Market I SEAWATER

The Oceans & Waves Steve Terrill/Stock Market

I. SEAWATER • Covers 71% of Earth’s surface • Nature of seawater – 35 o/oo dissolved salts (30 -38) – Varies from place to place • Origin of seawater – Volcanoes? – Comets? – Excess H+ & O-?

II. CURRENTS • Ocean water moves constantly sideways, up, down because it is: – Heated unevenly – Evaporated unevenly – Blown by wind – Affected by Earth’s rotation – Pulled by sun & moon • Currents are the flow of water between areas of different surface levels or different densities

Surface ocean currents are run by climate & rotation

Density Currents • Function of – Temperature (polar regions) – Salinity (Mediterranean Sea) – Suspended materials (turbidities- flow of muddy water down a slope) • Deep ocean currents move by – density & thermal differences – the Coriolis effect • NADW, AABW

Average surface salinity of the oceans

August sea-surface temperatures

Circulation of the Atlantic Ocean

CONVEYOR BELT

Turbidity Currents

III. Tides Twice daily rise and fall of the sea caused by the gravitational attraction between • earth and moon (lunar tides) • earth and sun (solar tides) Function of distance between and mass of the Earth, Moon and Sun

Interaction between lunar and solar tides during the lunar month causes: • Neap tides: when two tidal components are out-of-phase, hence lower than usual, and • Spring tides: when two tidal components are in-phase, hence higher than usual.

The highest and lowest tides occur due to the interaction of earth, moon, and sun

The effect of tides on a tidal inlet.

Mont-Saint-Michel France Exposed tidal flats Thierry Prat/Sygma

Terrace Exposed at Low Tide James Valentine

IV. WAVES • Waves are described by – Wave length(L): distance between crests – Wave height (H) : vertical distance between crest and trough – Wave period (T): time for successive waves to pass a fixed point – Wave velocity (V) of waves (V = L/T) • 2 kinds of waves – Deep water waves – Shallow water waves

Wind-generated Orbital Waves

Most waves are generated in the open ocean & • height depends on: – Wind velocity – Wind duration – Distance over which wind blows called the FETCH, usually a big storm.

Shallow water waves • At water depth of L/2, wave feels bottom. Then: • Wave height Increases as • Wave length decreases. • Velocity decreases because wave is dragging on bottom. • Period doesn’t change • When wave reaches 1. 3 H -> BREAKER

Wave refraction • Bending of wave crests as they approach the beach at an angle • Caused by the change in velocity of waves as a function of water depth • Only a small part of each wave feels bottom at a time so only a small part of wave slows.

Wave Refraction

Waves Bending as they Approach the Beach John S. Shelton

Sediment transport near shore, parallel to the beach • Longshore drift: drift sediment carried by swash and backwash along the beach • Longshore currents: currents parallel to the beach within the surf zone

Longshore Drift

V. COASTS • BEACHES • EROSIONAL COASTS -uplift • DEPOSITIONAL COASTS - sinking • CHANGES IN SEA LEVEL-relative

Refraction at Headlands and Bays

Carving a coast • Waves & currents act the same as streams except work in both directions • Erode - in high energy areas by – Abrasion – Solution – Wave pressure • Deposit -in low energy areas

Sandy Beach, North Carolina Barrier Island Peter Kresan

Boulder Beach, Massachusetts Raymond Siever

Major parts of beaches • Offshore: Offshore from where the waves begin to feel bottom to the surf zone • Foreshore: Foreshore includes the surf zone, tidal flats, and swash zone • Backshore: Backshore from beyond the swash zone to the highest level of the beach

Major Parts of a Beach

Sand Budget of a Beach

Factors determining rates of erosion or deposition • • • Uplift Subsidence Rock type Sea-level changes Storm wave heights Tidal range

Erosional Coasts • Region of up-lift - JOB IS TO STRAIGHTEN SHORELINE • Prominent cliffs & headlands • Narrow inlets, irregular bays & beaches • Undercut cliffs – Sea stacks – Wave-cut terraces • Falling sea level

Sea Stacks Kevin Schafer

Wave-cut Terrace Exposed at Low Tide John S. Shelton

Uplifted Coastal Terrace John S. Shelton

Depositional Coasts • Sinking coasts • Long, wide beaches – Bars – Spits – Barrier islands – Tidal flats & shallow lagoons • Low-lying, sedimentary coastal plains • Rising sea level - estuary

Southern Tip of Cape Cod Steve Durwell/The Image Bank

Partially Developed Barrier Island Mainland Florida Lagoon Barrier Island Gulf of Mexico Richard A. Davis, Jr

Effects of rising sea level: Eastern North America and Europe

VI. Preventing beach erosion • Structural approaches (e. g. , groins): typically cause increased erosion down current of structure • Non-structural approaches (e. g. , beach nourishment, land use planning): expensive, but don’t cause erosion in new areas

Erosion Deposition Phillip Plissin/Explorer Groin: Built to Prevent Updrift Erosion Causes Downdrift Erosion

Interrupting longshore currents

Beach Nourishment, New Jersey U. S. Corps of Engineers, New York District

From volcanic island to an atoll

Atoll Fringing Reef Guido Alberto Rosi/The Image Bank Some of the Maldive Islands in the Pacific

IX. Types of marine sediment • Terrigenous material eroded from the continents • Biochemically precipitated shells of marine organisms • Abiotic chemical precipitates • Extraterrestrial material

Oceanic Ooze Scripps Institute of Oceanography, University of California, San Diego

The END

Carbonate Compensation Depth below which carbonate material dissolves in seawater

Origin of the lunar tides

Changes in Waves as they Approach the Beach