Portion of the ocean affected by processes that occur on or near land (e.g., runoff, tidal currents, waves)
Open Ocean
Beyond the coastal zone
Coastal zone is usually defined as the area between coastline and shelf break
Coastal zone is 10% of total area of the oceans and harbors 99% of world fishery catch
Activities in the coastal zone
Harbors
Recreation
Mining of sand and other minerals
Oil exploration
Waste disposal
Coastal Waters
Relatively shallow-water areas that adjoin continents
Because of their proximity to land, coastal waters are influenced by processes that occur on or near land (e.g. river runoff or tidal currents) more than the open ocean
Characteristics of Coastal Waters
Temperature and salinity are more variable
Freshwater from river runoff + small vertical mixing → well-developed halocline (low to high salinity)
No river runoff + dry winds blowing from land + small vertical mixing → well-developed halocline (high to low salinity)
Low- and high latitude coastal waters → isothermal ("same temperature")
Mid-latitudes → well-developed thermocline (surface water warmer during summer and cooler during winter)
Vertical mixing may make thermocline less pronounced
Coastal Environments
Estuaries
Fjords
Lagoons
Beaches
Estuary
Partially enclosed coastal body of water in which freshwater from runoff dilutes salty ocean water
Origins of Estuaries
Coastal-plain estuary (former river valley now flooded with seawater)
Bar-built estuary (lagoon separated from open ocean by sand bars or barrier islands)
Tectonic estuary (faulting or folding of rocks creates a restricted down-dropped area which was flooded)
Fjord (former glaciated valley now flooded with seawater)
Estuarine Circulation
1. Surface flow of less dense freshwater toward the ocean
2. Opposite flow below the surface of salty seawater into the estuary
3. Vary with tidal currents mixing, wind-driven wave mixing, shape and depth of the estuary, rate of freshwater discharge, friction, Coriolis effect, human-made structures
Types of Estuarine Circulation
Vertically mixed (salinity uniform from surface to bottom)
Slightly stratified (two water layers can be identified, separated by zone of mixing)
Highly stratified (deep-water layer has uniform open-ocean salinity)
Salt wedge (wedge of salty water intrudes from the ocean beneath the river water)
Estuaries are important breeding grounds and protective nurseries for many marine mammals
Estuaries also support shipping, logging, manufacturing, waste disposal, and other activities damaging to the environment
Estuaries can be threatened both where human populations are modest (e.g. Columbia River estuary) or are large (e.g. Chesapeake Bay)
Columbia River Estuary
Salt-wedge estuary at its entrance to the Pacific ocean
Flow of river and tides drives a salt wedge as far as 42-km upstream, raising river level by 3.5-m
When tide falls, the huge flow of freshwater creates a freshwater wedge that can extend 100's of kms into the Pacific
Affected by interference with floodplains: dikes to prevent flooding of agricultural areas, logging has increased sediment load into the river, multiple hydroelectric dams have altered ecosystem, no salmon ladders to help fish "climb" around dams to reach their spawning grounds at headwaters
Chesapeake Bay Estuary
Fed by 19 major rivers and 400 creeks and tributaries
Slightly stratified
Seasonal changes in salinity, temperature and dissolved oxygen
Leads to development of a strong halocline and pycnocline preventing fresh surface water and saltier deep water from mixing
Anoxic conditions below pycnocline in summer as dead organic matter decays
Anoxia leads to major kills of commercially important marine animals (e.g. blue crab, oysters)
Degree of stratification and extent of mortality of bottom-dwelling animals has increased since 1950s
Tied to increased nutrients from sewage and agriculture fertilizers, increasing productivity of algae
In drier years with less river runoff, less widespread anoxia because less nutrients are supplied and less stratification
Fjord
Flooded glacial valley (u-shaped), tend to be deeper than adjacent seas, long narrow inlet with steep cliffs, sill (or shoal) often present near mouth, located on rugged mountainous coastlines
Deep water is dense (saline) and has limited mixing with layers above
Deep water can become anoxic (oxygen deprived)
Renewal of deep water determined by exchange flow over sill
Lagoon
Protected, shallow body of water, landward of barrier islands, form in bar-built estuaries, restricted circulation with the ocean, results in 3 zones: freshwater zone, transitional zone, saltwater zone
Beach
Deposit of the shore area, entire active areas of a coast that experiences changes due to breaking waves, wave deposited accumulation of sediment located at the shoreline, can be thought of as material in transit along the shoreline, area of beach above the shoreline is the "recreational beach"
Beach Glossary
Shore
Coast
Coastline
Backshore
Foreshore
Shoreline
Nearshore
Offshore
Beach
Berm
Beach face
Longshore bars
Shoreline
The water's edge (migrates with tides)
Shoreline
Can be thought of as material in transit along the shoreline
Area of beach above the shoreline is the "recreational beach"
Beach Glossary
Shore = zone between lowest tide level and highest elevation affected by storm waves
Coast = from shore to farthest point where ocean-related features can be found
Coastline = boundary between shore and coast
Backshore = above high tide, covered with water only during storms
Foreshore = zone between low and high tide
Shoreline = water's edge (migrates with tides)
Nearshore = from low tide shoreline to breaker line
Offshore = waves rarely affect the bottom
Beach = entire active area of a coast that experiences changes due to breaking waves
Berm = dry, gently sloping, slightly elevated margin of the beach (dry sand)
Beach face = wet sand, exposed during low tide
Longshore bars = sand bars parallel to the coast
Dissipative beach
Almost flat
Spilling breakers
Broad surf zone
Fine sediment
Reflective beach
Steep
Surging breakers
Narrow surf zone
Coarse sediment
Beach composition dependent on locally available material
Movement of sand on the beach occurs both perpendicular to the shore and parallel to the shore
Movement of sand perpendicular to the shore
1. Toward shore
2. Away from shore
Movement of sand parallel to the shore
1. Upcoast
2. Downcoast
Swash
Water rushes up the beach
Backwash
Water drains back to the ocean
Swash and backwash
Transport sediment up and down the beach face perpendicular to the shoreline
Whether swash or backwash dominate
Determines whether sand is deposited or eroded
Low-energy waves
Backwash is reduced, net transport of sand up to the beach face, well-developed berm
High-energy waves
Beach saturated with water from previous waves, backwash dominates, net transport of sand down the beach face, erodes the berm, sand accumulates beyond where the waves break, forms sand bars