1. The Marine Environment
Chapter 16

2. 16.1 Shoreline Features
Shorelines are shaped by the action of waves, tides and currents
As waves erode coastlines, they create impressive rock formations
Sometimes, waves drop/deposit loose sediments and build wide, sandy beaches
Waves move faster in deeper waters than they do in shallow waters
Wave refractions – difference in wave speed causing straight wave crests to bend when the crest moves into shallow water

3. Erosional Landforms
Rocky headlands – points of land sticking out into the ocean
Caused by the destructive action of breakers
Can be modified by wave erosion
Sea stacks / sea arches form from wave refraction at the rocky headland

4. Beaches
Sloping band of sand, pebbles, gravel, or mud at the edge of the sea
Composed of loose sediments deposited and moved about by waves along the shoreline

5. Beach Composition Depends on source of material
Hawaii – black sand/tiny grains of minerals from volcanic rocks
Southern Florida / Bahamas – white / pink sand from fragments of local corals and seashells
Near mouths of large rivers – sandy sediments washed in by river water, small grains of quartz and feldspar
Size of sediment particles depends on energy of waves striking the coast

6. Estuaries
The area where the lower end of a freshwater river or stream enters the ocean
Water is blackish in color
Water is a mixture of freshwater and saltwater
Nurseries to young of many different species
Examples include the Chesapeake Bay and the Pamlico Sound

7. Longshore Currents
Longshore bar – submerged sandbar located in the surf zone
Longshore current – current that flows parallel to the shore
Moves large amounts of sediments
Forms when incoming breakers spill over a Longshore bar

8. Longshore Currents (cont.)
Movement of Sediments
Longshore currents move large amounts of sediments along the shore
Fine-grained materials are suspended in turbulent, moving water
Large materials are pushed along the bottom of the current
Some sediments are pushed back and forth on the beach (incoming/outgoing waves)
Longshore transport is generally to the south
Rip Currents
Wave action produces rip currents, which flows out to the sea through gaps in the Longshore bar
Return the water spilled into the Longshore trough to the open ocean
Currents can reach speeds of several km/hr
One should never swim against rip currents, but should swim parallel to the shore to get out of the current

9. Depositional Features of Seashores
Most seashores are in a constant state of change
Sediments are eroded by large storm waves and are deposited where waves slow down

10. Sediments deposited build coastal landforms
Tombolo
Ridge of sand that forms between mainland and an island
Connects the island to the mainland
When this is present, it makes the island the “tip” of a peninsula
Lagoon
Shallow, protected body of water behind barrier islands
Essentially coastal lakes
Connected to sea by shallow, restricted outlets

11. Depositional Features of the Shoreline
Spit
Narrow bank of sand that projects into the water from a bend in the coastline
Forms where a shoreline changes direction
Protected from wave action
When growing spit crosses bay, baymouth bar forms
Barrier Islands
Long ridges of sand or other sediments
Deposited or shaped by longshore currents that are separated from mainlands
Can be several km wide / tens of km long
Unstable and temporary

12. Barrier Islands of North Carolina – The Outer Banks

13. Protective Structures
Structures are built to prevent beach erosion and destruction of oceanfront properties
Interfere with natural shoreline processes

14. Examples and Negative Effects of Protective Structures
Seawalls
Built along shore to protect oceanfront properties
Reflect waves back to the beach
Protect oceanfront properties
Worsens beach erosion
Groins
Wall-like structures build into the water perpendicular to the shoreline to trap beach sand
Interrupts natural longshore transport
Deprives beaches of sand down the coast

15. Examples and Negative Effects of Protective Structures
Jetties
Walls of concrete built to protect a harbor entrance from drifting sand
Jetties trap sand upshore
Prevents sand from reaching beaches downshore
Breakwaters
Built in the water parallel to straight shorelines to provide anchorages for small boats
Affects longshore currents causing them to no longer be able to move its load of sediment
Causes currents to drop and eventually build up to fill anchorage locations

16. Changes in Sea Level
Earth’s sea level rises and falls over time with changing of the Earth
Ice Age
Causes sea level to lower as the water freezes into ice caps
End of Ice Age
Causes sea level to rise due to the ice melting
Rise of Earth’s Surface Temperature
Causes seawater to warm up and expand
Adds total volume to the sea
Tectonic Movement (uplifting and sinking)
If a coastline sinks, rise in sea level along that coast
If a coastline rises, sea level along that coast drops
Emergent Coast – region that was formerly underwater
Tends to be relatively straight
Characterized by sandy beach ridges located far inland and elevated marine terraces

17. 16.2 The Seafloor
Until recently, most people had little knowledge of the features of the ocean floor. The topography of the seafloor is surprisingly rough and irregular, with numerous high mountains and deep depressions.

18. Oceanic and Continental Crust
As learned previously, the Earth has two types of crust:
Continental Crust – avg. thickness of 40km
Oceanic Crust – avg. thickness of 6-7km
Crustal elevation depends on crustal thickness, which is why thicker crust occurs on land and thinner crust occurs deep within ocean basins
Part of the continental section is actually below sea level and the ocean covers parts of the continents. These submerged portions are called continental margins and include the continental shelf, the continental slope and the continental rise.

19. Continental Shelves
The shallowest part of the continental margin, extending seaward from shore
The average width is 60km, although width varies greatly

20. Continental Slopes
Sloping regions where the seafloor drops away quickly, beyond the continental shelves
True edge of the continent
Often “cut” by submarine canyons, which are formed from turbidity currents

21. Continental Rise
Gently sloping accumulation of sediments dropped off by turbidity currents, forming at the base of the continental slope. This may be several km thick.

22. Ocean Basins
Deeper parts of the seafloor that lie above thin, basaltic, oceanic crust
Beyond the continental margin
Represents about 60% of the Earth’s surface

23. Topography of Ocean Basins
Abyssal Plains
Smooth parts of the ocean floor
5 or 6 km below sea level
Covered with hundreds of meters of muddy sediment
Probably flattest surfaces on Earth
Deep Sea Trenches
Deepest part of the ocean basins
Narrow, elongated depressions in the seafloor
Many lie next to chains of volcanic islands
Most located around margins of Pacific Ocean

24. Topography of Ocean Basins
Mid-Ocean Ridges
Most prominent features of ocean basin
Run through all ocean basins, total length of over 65,000km
Average height of 1500km, but varies
Sites of frequent volcanic eruptions and earthquake activity
Hydrothermal Vents
Hole in the seafloor through which fluid heated by magma erupts
Most located along bottom of rifts in mid-ocean ridges
“Black Smoker” or “White Smoker” classification, depending on what is ejected from the vent

25. Seafloor Volcanoes Mountains are found all throughout the seafloor
Believed to be extinct volcanoes, rather than mountain ranges
Two types:
Seamounts
Submerged basaltic volcanoes more than 1km high
Many stretched across the Pacific Ocean Basin
Guyots
Also called “tablemounts”
Large, extinct basaltic volcanoes with a flat, submerged top

26. Marine Sediments Come from a variety of sources, most from continents
Includes mud and sand washed into oceans by rivers, as well as volcanic ash blown over the ocean by winds

27. Types of Marine Sediments
Manganese Nodules
Major source of deep-sea sediment (shells and hard parts of marine animals)
Typically accumulate at a rate of a few mm per thousand years
Most are small, consisting of either calcium carbonate or silica
Ooze
Consist of oxides of manganese, iron, copper, and other valuable metals
Growth rates are incredibly slow
Measured in mm per million years