This document summarizes key features and characteristics of the ocean floor and seafloor landscapes. It describes major topographic features including mid-ocean ridges, abyssal plains, trenches, islands, seamounts, and continental margins. It also explains geological processes that shape the seafloor over time such as plate tectonics, sediment deposition, and turbidity currents. Modern technologies like sonar, seismic reflection profiling, and remote sensing have enabled detailed mapping and study of the diverse and globally significant seafloor environments.

1. Contamination of
GroundwaterGroundwater is critically important to humans since it is a major source
of drinking water.
Major threats to groundwater include spillage from underground
storage tanks, effluent from septic tanks and leachate from agricultural activities,
municipal landfills and abandoned hazardous waste sites (nitrates, volatile
organic compounds, petroleum products, metals and synthetic organic chemicals.
Once contaminated, groundwater is difficult and expensive, in many
cases impossible to rehabilitate.

3. Seawater
Seawater covers about 70 percent of the earth’s surface. The
average depth of the oceans is about 4 km.
The saltiness of the sea is measured in terms of its salinity, which is
commonly expressed in parts per thousand (ppt). The salinity of average
seawater is 35 ppt (equivalent 3.5%). The principal substances that
contribute to the salinity of seawater are sodium and chloride ions.
Seawater is a source of:
food and minerals
phosphate( an important fertilizer needed in agriculture and the land
supplies are being depleted)
Manganese
iron
copper
cobalt
Nickel

4. Seawater contains enough deuterium to make it a
feasible source of energy.
The sea may provide new sources of food through
aquaculture, the farming of the sea the way that the land is
presently farmed. Some aquaculture projects have already
started with the farming of oysters, clams and certain fishes.

5. Ocean and Seas
The body of salt water that covers the earth’s surface is called
the ocean, or the sea.
The principal regions are:
Atlantic Ocean- is second in size, with a surface area of 107 million km-
2 and the shallowest average of 3.3 km.
Indian Ocean- has the smallest surface area , with 74 million, and an
average depth of 3.8 km
Pacific Ocean- is the largest of the three principal ocean regions. It
covers 180 million km2. It is circled by active converging plate
boundaries, so it is sometimes described as being circled by a “rim of
fire”.

6. Pacific
Ocean
Indian
Ocean
Atlantic
Ocean

7. The Nature of Seawater
Sodium (table salt)
Chlorine (sodium chloride)
Most abundant ions:
The concentration is increased by two factors:
Evaporation- increases the concentration because only water vapor evaporates,
leaving the dissolved salts behind in greater concentration.
Formation of sea ice- ice that form from freezing seawater increases the
concentration because when ice forms the salts are excluded from the crystal
structure. Thus, sea ice is fresh water and the removal of this water leaves the
dissolved salts behind in greater consumption.

8. The salinity of seawater is decreased by
Heavy precipitation
melting of ice
addition of fresh water by a large river
The ocean basin has not become filled in by the continuous
supply of sediments and dissolved materials that would accumulate over
millions years. The reasons for this are:
accumulated sediments have been recycled to the earth’s interior
through plate tectonics
dissolved material are removed by natural processes just as fast as
they are supplied by the rivers.

9. Movements of
Seawater
Seawater is in constant state of motion, both on the surface and deep within.
The surface has two types of motion:
Waves, which have been produced some disturbance, such as the wind.
Waves travel across the surface as a series of wrinkles that range form few
centimeters high to more that 30m high. Waves crash on the shore as
breakers and make the surf.
Currents, which move water from one place to another

10. Wave
Currents

11. Waves
Gentle wind produces ripples on the surface of the ocean.
Continuous wind produces larger and longer-lasting ripples. A
ripple may eventually grow into an ocean wave, a moving disturbance
that travels across the surface of the ocean.
Each wave has a ridge, or mound of water called a crest,
which is followed by a depression called a trough.
Movement of the earth’s crust or underwater landslides can
produce giant destructive waves called tsunamis.
The basic pattern of two high tides and two low tides every
twenty-hours and fifty minutes can produce strong tidal currents in
narrow bays.

12. crest
trough

13. Tsunami

14. Ocean Tides
Seawater moves in continuous ocean currents,
streams of water that stays in about the same path as
they move through other seawater over large distances.
Oceans currents are produced by:
1. density differences in seawater
2. winds that blow persistently in the same direction

15. Density Currents
The density of seawater is influenced by three factors:
the water temperature
salinity
suspended sediments
The changes in the density of water result in the ocean
current known as density current.
Surface Currents
These are broad and deep-running ocean currents that
slowly move tremendous volumes of water relatively near the surface.
The currents are modified by other factors such as the
rotation of the earth and the shape of the ocean basins, but they are
basically maintained by the wind systems.

16. Each ocean has a great system of moving water called
gyre that is centered in the mid-latitudes.
The gyres rotate to the right in the Northern
Hemisphere and to the left in the Southern Hemisphere
because of the Coriolis Effect.
All are called “currents” except one that is called a
“stream” (the Gulf Stream) and those that are called “drifts”.

17. The Ocean Floor
The landscape of the ocean floor remained largely a mystery
until the development of modern oceanographic research.
The regional landscape of the seafloor can now be studied
with a variety of new instruments, including echo sounder, side scan
sonar images, magnetometers and seismic reflection profiles.
Seismic Reflection Profiles
The seismic reflection profile illustrates the type of information
obtained about the seafloor by seismic reflection. The method involves
emitting pulse of sound form a ship that is subsequently reflected back
from the seafloor.

18. Ocean Floors

19. Seismic Reflection Profiles

20. The Oceanic Ridge
The oceanic ridge is the most pronounced tectonic
feature on earth. If the ridge were not covered with water, it
would be visible from as far away as the moon. It is essentially
a broad, fractured swell, generally more than 1500 km wide,
with peaks rising as much as 3 km above the surrounding
ocean floor. It covers nearly 23 percent of the earth’s surface,
almost as much as the surface of the continents. It is the
greatest “mountain” system on earth.

21. Mid-ocean
Ridge

22. The Abyssal Floor
Vast areas of the deep ocean consist of broad relatively smooth surfaces
known as the abyssal floor.
In most ocean basins, the abyssal floor can be subdivided into two sections:
abyssal hills- are relatively small hills, rising from 75 to 900m above the ocean
floor. They are circular or elliptical and range from 1 to 8 km in width at the
base. The abyssal hills can be considered as the most widespread landform on
earth.
abyssal plains- are exceptionally flat areas of the ocean floor where the abyssal
hills are completely buried by sediment. They are located near the margins of a
continent, where turbidity currents transport sediment from a continental mass
and spread over the adjacent ocean floor.

23. The Abyssal
Floor

24. Trenches
A subduction zone, where two plates converge and one slab of
lithosphere plunges down into the mantle, is generally expressed
topographically by a trench.
A subduction zone is characterized by intense volcanic activity and
seismicity. It is also marked by a large gravity anomaly. Trenches, some of
which reach nearly 11,000 m below sea level, are the deepest parts of the
ocean floor.

25. Trench
Japan
Trench
Deep-Sea
Trench

26. Island and Seamounts
Thousands of submarine volcanoes occur on the ocean floor, with the
greatest concentration in the western pacific. Some rises above sea level and
form islands, but most remain submerged and are called seamounts.
They often occur in groups or chains, with individual volcanoes being
as much as 100 km in diameter and 1000 m high.

27. Islands and Seamounts

28. Continental Margins
The continental margins are covered by the ocean but are not
geologically part of the oceanic crust. They are composed of the
continental crust and sediment derived from erosion of the land.
This part of the seafloor can be divided into three major sections:
continental shelf- is simply a submerged part of the shield or stable
platform. It can be as much as 1500 km wide and its depth ranges from
20 to 550 m at its outer edge. At present, the continental shelves
comprise 18% of the earth’s total continental area.
continental slope- descends from the outer edge of the continental
shelf as a long, continuous slope to the deep-ocean basin. It marks the
edge of continental granitic rock mass, the boundary between the
continent and the ocean.

29. continental rise- is the transition between the continent and the ocean
basin. It has a gentle, inclined surface, rising from the abyssal plains to the
continental slope. It is apparently formed by sediment deposited at the
base of the continental slope.

30. Submarine Canyons
Submarine canyons are common along the continental slope and
have been studied for many years, long before the ocean floor was
mapped. They have V-shaped profile and a system of tributaries; they
closely resemble the great canyons cut by rivers on the continents.
Turbidity currents flowing from the continental shelf to the
abyssal floor usually cut submarine canyons. Turbidity canyons can move
at rates ranging up to 95 km per hour and carry a large sediment load
capable of vigorous erosion.

31. Deep-Sea
Trench