Characteristics of Coastal Waters

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

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

Temperature Variations in the Coastal Ocean

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

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

Characteristics of Coastal Waters

Estuaries Origin of estuaries – sea level rise after glacier retreat began 18,000 years ago Four types of estuaries based on geologic origin

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

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

Estuaries Classified by Geologic Setting

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

Classifying Estuaries by Mixing

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

Estuaries and Human Activities Columbia River Estuary Principal conduit for logging industry More than 250 dams constructed Increased sediment load Dredging of sediment carries increased pollution risk

Estuaries and Human Activities Chesapeake Bay Slightly stratified estuary Large seasonal changes in salinity, temperature, and dissolved oxygen Maximum freshwater river flow in spring

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

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

Lagoons Laguna Madre – along Texas coast Hypersaline Large seasonal temperature and salinity variations Ocean water flows in wedge over denser lagoon water

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

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

Mediterranean Sea

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

Mediterranean Circulation

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

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

Types of Coastal Wetlands Mangroves Tropics below 30 degrees latitude Salt-tolerant mangrove trees, shrubs, and palms Tall tripod-like root systems Caribbean, Florida, Southeast Asia

Distribution of Salt Marshes and Mangroves

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.

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

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

Serious Loss of Valuable Wetlands