Coastal Waters and Marginal Seas
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Transcript Coastal Waters and Marginal Seas
Coastal Waters and Marginal
Seas
Salinity
Runoff from rivers does not mix well with coastal
waters, so a well developed halocline forms
Though when shallow enough it will mix making it
isohaline
Temperature
Sea ice forms in high latitudes, while a strong
thermocline prevents water to mix in low latitudes
Mixing allows water to bring oxygen from the surface
to deeper water
Offshore winds can carry heat in the summer, or take
away heat during the winter
Coastal geostrophic currents
Geostrophic currents can form as wind blowing
parallel to shore piles water up
Gravity then pulls it back towards the ocean
Then as it runs back the coriolis effect takes over and
pulls it to the right or left
Even runoff is affected by the coriolis effect
Estuaries
Estuary is a partially enclosed body of water in which
freshwater runoff dilutes salty ocean water
Most common type is at the mouth of a river
Also most economically important due to being seaports
Experience great variations in temperature and
salinity
Classified by both origin and water mixing
Origin of estuaries
Coastal plain- formed when sea level rises and flood
river valleys
Fjord- formed when valleys carved by glaciers are
flooded
U shaped
Moraine- submerged glacial deposit of debris at the
mouth of the estuary marks the farthest extent of the
glacier
Origin of estuaries
Bar built estuary- formed from the opening between
a lagoon of a sand bar and the ocean
Tectonic estuary- formed when faulting or folding of
rocks creates a lower area where a river flows
Water mixing in estuaries
Vertically mixed estuary- the waters are mixed so
salinity just increases as one moves toward the ocean
Slightly stratified estuary- Somewhat deeper, like
vertically mixed but two water masses can be
identified
Water masses separated by a zone of mixing
The flow of low salinity surface water towards the
ocean and subsurface high salinity water towards the
river is estuarine circulation pattern
Water mixing in estuaries
Highly stratified estuary- strong separation between
the two water masses
deep estuary
well developed estuarine circulation
strong halocline
Salt wedge estuary-salt water intrude beneath the
river
Typical of high output rivers
Estuaries and human activities
Colombia river valley
Between Washington and Oregon
Many dams have altered the flow of the river
Salt wedge
Chesapeake Bay estuary
Formed by drowning of Susquehanna river
Slightly stratified
Water can become anoxic due to waters not mixing well
Coastal wetlands
Wetlands are in which the water table is close to the
surface, so they are saturated most of the time
Very productive and economically beneficial when left
alone
Most important types are salt marshes and mangrove
swamps
Both periodically covered by ocean water
Both have oxygen poor mud
Coastal wetlands
Can filter water very well, .4 acres can filter 2,760,000
liters of water
They are being destroyed
87 mil hectares to 43 mil hectares
Office of Wetland protection created to stop this
Lagoons
Lagoons lie between sand bars and land
Brackish
Salinity is high at the mouth but low at the head of the
river feeding it
Can be hyper saline in arid regions
Marginal seas
Marginal seas are margins of the ocean semi enclosed
isolated bodies of water
Mediterranean sea
Number of seas connected by small necks
Remains of Tethys sea
Contains an underwater ridge called a sill between sicily
and Tunisia
Mediterranean circulation
Atlantic water flows on the surface to replace water
evaporated in the arid eastern end
Water flows into the Atlantic at 200-600 meters of depth
The water cools to 13*C and 373% salinity as it passes though
the Gibraltar
It then goes down to 1000 meters and equalizes wih
surrounding water
Mediterranean circulation is where surface water from the
ocean replaces evaporated water in the mediterranean
Marginal seas
Marginal seas of the Atlantic
Mediterranean
Caribbean sea
Gulf of Mexico
Marginal seas of the Pacific
Gulf of California
Bering Sea
Marginal Seas
Marginal seas of the Atlantic
Red sea
Arabian sea
Bay of Bengal