Transcript Characteristics of Coastal Waters

Characteristics of Coastal Waters
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Characteristics of Coastal Waters
• Salinity – freshwater runoff does not mix well with
coastal seawater
• Halocline – represents salinity variations with
depth in water column
• Isohaline – uniform salinity from surface to
deeper layers
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Characteristics of Coastal Waters
• Temperature – coastal region surface water has
restricted mixing
• Isothermal – water temperature is uniform
throughout water column
• Thermocline – represents temperature
variations with depth
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Temperature Variations in the Coastal
Ocean
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Characteristics of Coastal Waters
• Coastal Geostrophic Currents
– Move in circular path
– Generated in coastal areas by wind and runoff
• Wedge of freshwater runoff on coast generates
surface flow towards open ocean
– Coriolis effect deflects flow
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Characteristics of Coastal Waters
• Coastal Geostrophic Currents
• Northern Hemisphere – path curves northward on
western coasts and southward on eastern coasts
– Opposite in Southern Hemisphere
• Davidson Current – coast of Washington and
Oregon
– More strongly developed during rainy season
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Characteristics of Coastal Waters
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Estuaries
• Origin of estuaries – sea level rise after glacier
retreat began 18,000 years ago
• Four types of estuaries based on geologic origin
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Estuaries
• Coastal plain estuary – forms as sea level rises
and floods existing river valleys
– Chesapeake Bay
• Fjord – forms as sea level rises and floods
existing glaciated valleys
– Coasts of Alaska, Canada, New Zealand, Chile, and
Norway
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Estuaries
• Bar-built estuary – shallow and separated from
open ocean by sand bars deposited parallel to
coast by wave action
– U.S. Gulf coast and East Coast
• Tectonic estuary – forms when folding or faulting
rocks generates downdropped area
– San Francisco Bay
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Estuaries Classified by Geologic Setting
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Water Mixing in Estuaries
• Vertically mixed estuary – shallow, low-volume.
Net flow from head to mouth of estuary
• Slightly stratified estuary – salinity increases
from head to mouth at all depths. Two distinct
layers
• Highly stratified estuary – deep with upper-layer
salinity increasing from head to mouth
• Salt wedge estuary – wedge of salty water from
ocean moves in under river water
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Classifying Estuaries by Mixing
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Estuaries and Human Activities
• Most threatened where human populations are
large
• Estuaries are important breeding grounds and
nurseries for many marine animals
• Human activities can damage estuarine
environments
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Estuaries and Human Activities
• Columbia River Estuary
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Principal conduit for logging industry
More than 250 dams constructed
Increased sediment load
Dredging of sediment carries increased pollution risk
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Estuaries and Human Activities
• Chesapeake Bay
– Slightly stratified estuary
– Large seasonal changes
in salinity, temperature,
and dissolved oxygen
– Maximum freshwater river
flow in spring
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Estuaries and Human Activities
• Chesapeake Bay
– Waters may become anoxic from May through August
– Major kills of commercially important blue crabs,
oysters, and other bottom-dwelling organisms
– Increased nutrients from sewage and agriculture
causing algal blooms and environmental issues
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Lagoons
• Protected, shallow water
bodies landward of
barrier islands
• Restricted circulation
with ocean
• Three distinct zones
– Freshwater zone near
head
– Transitional zone in
middle
– Saltwater zone near
mouth
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Lagoons
• Laguna Madre – along
Texas coast
– Hypersaline
– Large seasonal
temperature and salinity
variations
– Ocean water flows in
wedge over denser
lagoon water
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Marginal Seas
• Large semi-isolated bodies of water
• Result from tectonic events that isolated ocean
crust between continents or created behind
volcanic island arcs
– Mediterranean Sea
– Caribbean Sea
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Mediterranean Sea
• Remnant of ancient Tethys Sea
• Shallow and narrow connection to Atlantic Ocean
and Black Sea
– Strait of Gibraltar
– Bosporous
• Underwater sill separates Mediterranean into two
major basins
– Sill restricts flow, resulting in strong currents
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Mediterranean Sea
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Mediterranean Sea
• Mediterranean Circulation
– Unique pattern caused by Middle East heat
– Large surface inflow from Atlantic Ocean to replace
evaporated surface water flows along north African
coast, spreads
– Remaining Atlantic water flows eastward to Cyprus
– Water sinks and becomes Mediterranean Intermediate
Water
• Temperature of 15oC (59oF) and salinity of 39.1 ppt
• Flows westward at depth of 200 to 600 m (660 to 2000 ft)
– Temperature drops as it reaches Gibraltar
• Mediterranean Circulation is opposite that of most
estuaries
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Mediterranean Circulation
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Issues Facing Coastal Wetlands
• Wetlands – ecosystems with water table close to
surface
– Generally saturated
– Can be freshwater or coastal
• Coastal wetlands occur along margins of costal
waters, including estuaries, lagoons and marginal
seas
– Include swamps, tidal flats, coastal marshes, and
bayous
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Types of Coastal Wetlands
• Salt marshes
– Between 30 and 65 degrees latitude
– Support salt-tolerant grasses and other halophytic
low-lying plants
– Along many coasts
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Types of Coastal Wetlands
• Mangroves
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Tropics below 30 degrees latitude
Salt-tolerant mangrove trees, shrubs, and palms
Tall tripod-like root systems
Caribbean, Florida, Southeast Asia
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Distribution of Salt Marshes and Mangroves
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Characteristics of Coastal Wetlands
• Home to diverse plants and animals
• Highly productive ecosystems
• Nurseries for more than half of commercially
important fish species in southeastern U.S.
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Characteristics of Coastal Wetlands
• Soak up nutrients that run off farmlands
• Remove inorganic nitrogen compounds and
metals from environment
• Protect shorelines from erosion
• Dissipate coastal wave energy
• Absorb excess water
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Serious Loss of Valuable Wetlands
• More than half of U.S. wetlands have vanished
• Filled in and developed
• U.S. Environmental Protection Agency (EPA)
established Office of Wetlands Protection (OWP)
in 1986
• Future sea level rise predicted to exacerbate
wetland loss
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Serious Loss of Valuable Wetlands
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