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Oceanography 100
P Anderson
Chapter 11
The Coastal Ocean
Coastal waters
• Relatively shallow areas that adjoin continents
• Heavily used for commerce, recreation, fisheries, and waste disposal
• Experience dramatic changes in salinity and temperature
Salinity and temperature in the coastal ocean
Estuaries
• Estuaries are partially enclosed coastal bodies of water
• Examples of estuaries include:
– River mouths
– Bays
– Inlets
– Gulfs
– Sounds
• Formed by a rise in sea level after the last Ice Age
Classifying estuaries by origin
• Coastal plain
• Fjord
• Bar-built
• Tectonic
Examples of estuaries
Classifying estuaries by water mixing
• Vertically mixed
• Slightly stratified
• Highly stratified
• Salt wedge
Coastal wetlands
• Coastal wetlands are saturated areas that border coastal environments
• Brackish water conditions
Salt marshes and mangrove swamps
• Two most important types of coastal wetlands:
– Salt marshes (mid-latitudes)
– Mangrove swamps (low latitudes)
The value of coastal wetlands
• Coastal wetlands are highly productive areas that serve as fish nurseries for many
important species
• Effectively filter polluted runoff from land
• Problem: are viewed as worthless land, so are often replaced with developments
(roads, housing, shopping, etc.)
Lagoons
• Lagoons are shallow coastal bodies of water separated from the ocean by a narrow
strip of land such as a barrier island
Mediterranean circulation
• The Mediterranean Sea experiences high rates of evaporation
• Causes inflow of water at the surface and outflow of high salinity water below
Pollution in coastal waters
• Coastal waters are highly affected by pollution because they are:
– Heavily used
– Close to sources of pollution
– Shallow-water bodies
– Not as well circulated as the open ocean
Marine pollution: A definition
• The introduction by man, directly or indirectly, of substances or energy into the marine
environment, including estuaries, which results or is likely to result in such deleterious
effects as harm to living resources and marine life, hazards to human health, hindrance
to marine activities, including fishing and other legitimate uses of the sea, impairment
of quality for use of sea water and reduction of amenities. (World Health
Organization)
Main types of marine pollution
• Petroleum (oil)
• Sewage sludge
• DDT and PCBs
• Mercury
• Non-point-source pollution
Marine pollution: Petroleum
• Oil spills can be caused by:
– Tanker accidents
– Intentional dumping
– Drilling/pumping operations
Marine pollution: Petroleum
• Petroleum is biodegradable
• Many pollution experts consider oil to be among the least damaging ocean pollutants
• Data from the 1989 Exxon Valdez oil spill shows the recovery of key organisms
• Various processes act to break up and degrade oil in the marine environment
• When oil washes up at a beach, it can negatively affect the marine environment
• Oil can coat marine organisms and render their insulating fur or feathers useless
Marine pollution: Sewage sludge
• Sewage sludge is the semisolid material that remains after sewage treatment
• Much sewage sludge was dumped offshore until laws restricted sewage dumping
Marine pollution: DDT
• DDT was a widely used pesticide that became concentrated in marine fish
• DDT caused brown pelicans and ospreys to produce thin egg shells
• Worldwide, DDT has been banned from agricultural use but is still used in limited
quantities for public health purposes
Marine pollution: PCBs
• PCBs are industrial chemicals used as liquid coolants and insulation in industrial
equipment such as power transformers
• PCBs enter the marine environment through leaks and from discarded equipment
• PCBs can accumulate in animal tissues and affect reproduction
Marine pollution: Mercury and Minamata disease
• Mercury has many industrial uses but is extremely toxic
• A chemical plant released large quantities of mercury into Minamata Bay, Japan
• Residents who ate highly contaminated fish suffered neurological disease and birth
disorders (Minamata disease)
Marine pollution: Non-point- source pollution
• Non-point-source pollution comes from material washed down storm drains as “poison
runoff”
• Includes fertilizers, pesticides, road oil, and trash
Current law regulating ocean dumping
• The only substance that is illegal to dump anywhere in the ocean is plastic
Plastic in the marine environment
• Plastic:
– Does not biodegrade
– Floats
– Has high strength
– Is ingested by and entangles marine animals