Earth
Science, 10th edition
Chapter
13: Ocean Water and Ocean Life
I. Composition of seawater
A. Seawater consists of about 3.5% (by
weight) dissolved minerals
B. Salinity
1. Total amount of solid material
dissolved in water
2. Typically expressed in
parts-per-thousand (‰)
3. Average salinity is 35‰
4. Major constituent is sodium
chloride
C. Sources of sea salts
1. Chemical weathering of rocks
2. Outgassing
– gases from volcanic eruptions
D. Processes affecting seawater salinity
1. Variations in salinity are a
consequence of changes in the water content of the solution
2. Processes that decrease salinity
(add water)
a. Precipitation
b. Runoff from land
c. Icebergs melting
d. Sea ice melting
3. Processes that increase salinity
(remove water)
a. Evaporation
b. Formation of sea ice
4. Surface salinity in the open
ocean ranges from 33‰ to 38‰
A. Surface water temperature varies with
the amount of solar radiation received
1. Lower surface temperatures are
found in high-latitude regions
2. Higher temperatures found in
low-latitude regions
B. Temperature variation with depth
1. Low-latitudes
a. High temperature at the
surface
b. Rapid decrease in
temperature with depth (thermocline)
2. High-latitudes
a. Cooler surface temperatures
b. No rapid change in
temperature with depth
C. Ocean temperature over time
1. The unique thermal properties of
seawater make it resistant to temperature changes
2.
Global warming could eventually influence ocean temperatures
A. Density is mass per unit volume - how heavy
something is for its size
B. Determines the water’s vertical
position in the ocean
C. Factors affecting seawater density
1. Salinity
2. Temperature - the greatest
influence
D. Variations with depth
1. Low-latitudes
a. Low density at the surface
b. Density increases rapidly
with depth (pycnocline) because of colder water
2. High-latitudes
a. High-density (cold) water
at the surface
b. Little change in density
with depth
E. Ocean layering
1. Layered according to density
2. Three-layered structure
a. Surface mixed zone
1. Sun-warmed zone
2. Zone of mixing
2. Shallow (300 meters)
b. Transition zone
1. Between
surface layer and deep zone
2. Thermocline
and pycnocline
c. Deep zone
1. Sunlight never reaches
this zone
2. Temperatures are just a
few degrees above freezing
3. Constant high density
water
3. Three-layer structure does not
exist in high-latitudes
A. Marine environment is inhabited by a
wide variety of organisms
B. Most organisms live within the
sunlight surface waters (photosynthesis)
C. Classification of marine organisms
1. Plankton
a. Floaters
b. Algae (phytoplankton)
c. Animals (zooplankton)
d. Bacteria
e. Most of Earth’s biomass
2. Nekton
a. All animals capable of
moving independently of the ocean currents
b. They are unable to move
throughout the breath of the ocean
3. Benthos
a. Bottom dwellers
b. A great number of species
exist on the shallow coastal floor
c. Most live in perpetual
darkness in deep water
D. Marine life zones
1. Several factors are used to
divide the ocean into distinct marine life zones
a. Availability of light
1. Photic
(light) zone
a. Upper part of
ocean
b. Sunlit
c. Euphotic zone is near the surface where the light is strong
1. Phytoplankton
use sunlight to produce food
2. Different
wavelengths of light are absorbed at different depths
2. Aphotic
(without light) zone
a.
Deep ocean
b. No sunlight
b. Distance from shore
1. Intertidal
zone – area where land and ocean meet and overlap
2. Neritic
zone – seaward from the low tide line, the continental shelf out to
the shelf break
3. Oceanic zone – beyond
the continental shelf
c. Water depth
1. Pelagic zone – open ocean of any depth
2. Benthic zone – includes
any sea-bottom surface
3. Abyssal zone – a
subdivision of the benthic zone
a.
Deep
b. Extremely high
water pressure
c. Low temperatures
d. No sunlight
e. Sparse life
f. Food sources
1. Decaying
particles from above
2. Large
fragments falling
3. Hydrothermal
vents
V. Oceanic Productivity
A. Related to primary productivity
1. The amount of carbon fixed by
organisms through the synthesis of organic matter
2. Sources of energy
a. Photosynthesis (solar
radiation)
b. Chemosynthesis (chemical
reactions)
3. Influenced by
a. Availability of nutrients
b. Amount of solar radiation
4. Most abundant marine life exists
where there is ample
a. Nutrients, and
b. Good sunlight
B.
Productivity in polar oceans
1. Because of nutrients rising from deeper water,
high-latitude surface waters have
high
nutrient concentrations
2. Low solar energy limits
photosynthetic productivity
C. Productivity in tropical oceans
1. Low in the open ocean
2. Thermocline
eliminates the supply of nutrients from deeper waters below
D. Productivity in temperate oceans
1. Winter
a. Low productivity
b. Days are short and sun
angle is low
2. Spring
a. Spring bloom of
phytoplankton is quickly depleted
b. Productivity is limited
3. Summer
a. Strong thermocline
develops so surface nutrients are not replaced from below
b. Phytoplankton population
remains relatively low
4. Fall
a. Thermocline
breaks down and nutrients return to the surface
b. Short-lived fall bloom of
phytoplankton
E. Highest overall productivity occurs in
temperate regions
VI. Oceanic feeding relationships
A. Main oceanic producers
1. Marine algae
2. Plants
3. Bacteria
4. Bacteria-like archaea
B. Only a small percentage of the energy
taken in at any level is passed on to the next
C. Trophic levels
1.
Chemical energy stored in the mass of the ocean’s algae is transferred to the
animal community
mostly through feeding
2.
Each feeding stage is called a trophic level
D. Transfer of energy between trophic levels is very inefficient (about 2%)
E. Food chains and food webs
1. Food chain - a sequence of
organisms through which energy is transferred
2. Food web
a.
Involves feeding on a number of different animals
b. Animals that feed through a
food web rather than a food chain are more likely to survive