chapter 13 the oceans, coastal processes, and landforms

Chapter 13The Oceans, Coastal

Processes, and Landforms

Humans have always been drawn to the sea

- Commerce and access to sea routes, fishing, and tourism prompt many people settle near the ocean.

- 40% of Earth population lives within 100 km of coastlines… 50% of U.S. population are classed as coastal

Understanding coastal processes and landforms is important to billions worldwide… processes and landforms are significant to planning

and management

Global Oceans and Seas

Why are the oceans important?

(1) the Earth surface is approximately 72% water

(2) Their role in: hydrologic cycle;

distribution of solar energy; CO2 sink;

generation of pressure systems; food source; habitat; minerals; pollution

dispersion; etc

Figure 13.1

Chemical Composition of Seawater- Most naturally occurring elements and the compounds

that they form are found as dissolved solids (solutes) in seawater

- Seawater is a chemical solution and the concentration of dissolved solids is salinity

- Ocean salinity displays only minor variation globally as do concentrations of individual mineral solids

[a function of circulation patterns and the

inter-connected-ness of ocean basins]

Ocean Chemistry- Text: “Ocean chemistry is the result of complex

exchanges among seawater, the atmosphere, minerals, bottom sediments, and living organisms.” (p. 422)

- Additionally, we are now aware of significant mineral import at “black smoker” sites

- Seven elements account for more than 99% of seawater dissolves solids (ionic forms of):chlorine sodium* magnesium*

sulfur calcium potassiumbromine*

* Harvested in significant / commercial levels

Average Salinity: 35%o

- Text tells us that salinity (dissolved solids by volume) can be reported in several manners… with the most common being in parts/thousand (%o)

- Globally ocean salinity varies between 34%o and 37%o

- variations come about through: (1) atmospheric conditions

and/or (2) volume of freshwater inflows

--- Equatorial waters with more precipitation tend to lower saline concentrations (<35 %o) brackish

--- Subtropical waters with greater evaporation tend to greater salinity (>35 %o) brine

--- ocean areas and estuaries contiguous to continents tend toward brackish conditionsas do areas of tropical storms and hurricanes (freshwater inflows and rainfall)

--- enclosed bays with little circulation tend toward brine conditions

--- more salinity=greater density… deep saline pockets

Coastal System Components- Continental features formed over millions of years…

most coastlines are new and constantly changing

- Endogenous and exogenous factors

insolation wind/precipitation climate; structure and form of rock material

human activities gravity

act together to produce tides, currents, waves, erosin / deposition

The Coastal Environment and Sea Level- The coastal zone is termed the littoral zone

--- it is an interface zone between land and water--- in-land as far as the high water level / seaward to the

point that storms cannot eject ocean-borne materials / sediments to shore (approx. 60m depth)

- shoreline: contact line between sea and shore- coast: adjacent land area- sea level: relative term; no exact value - Mean sea level (MSL): av. tidal levels recorded hourly at a

site for at least 19 yrs…overall MSL measured at 40 sites along N.A. coast

Littoral Zone

Figure 13.3

Coastal System Actions  Tides - daily oscillations in sea levels … variable from barely

noticeable to several meters  Causes of tides – the gravitational interactions of the Earth,

Moon, Sun --- situations that combine into strong gravitational

forces result in Spring [Fig 13.5 (a) and (b)] tides --- situations where gravitational forces do not act

together result in neap tides [Fig 13.5 © and (d)]--- tidal power generating energy from the rise and

fall of tides [not that difference from falling water generation if you think of each tide cycle as a new local baseline level]

Tides

Figure 13.5

Figure 13.6

Tidal Range

andTidal

Power

Coastal System Outputs  Erosional Coastal Processes and Landforms- tides, currents, wind, wave action and sea level change make

coastlines active continental margins… energy and sediment are constantly being transferred into a narrow environment--- erosional coastlines - associated with Pacific NW tend to

ruggedness, high cliffs and active plate tectonics--- sea cliffs – form from the undercutting action of waves

which ultimately causes collapse … such coastlines might include: sea caves, sea

arches and sea stacks--- wave-cut platform – horizontal terraces cut from sea cliff

to the sea… multiple terraces can be cut as water level rises and falls

Erosional Features

Figure 13.10

Depositional Coastal Processes and Landforms

- Generally associated with coastal areas of gentle relief

--- characteristic is a barrier spit which extends outward from the shore in a long submarine ridge

… can develop further into a bay barrier (baymouth spit) which cuts off a

bay; forming a lagoon

… can growth perpendicular to the shore as a tombobob connecting the hore to a

sea stack

Depositional Coastal Features

Figure 13.11

Beaches- That area along a coast where the shoreline is in motion

and modified by deposition by wave and current- Text: the beach zone on average, ranges from 5 m above

high tide to 10 m below low tide… great variability exists

- dominated by SiO2 (quartz) sand

- several forms of beach: shingle beach (gravel/shells) rocky beach (self-explanatory)

- Parallel off-shore beaches are protective barrier beaches

Littoral DriftFigure 13.12

NC Barrier Islands

Figure 13.13

Biological Processes: Coral Formations- In addition to physical processes, organic agents and

processes can impact coastline formation… coral

- coral is a simple marine animal composed of a soft sack-like body (apolyp) which secretes a CaCO3 outer skeleton both for protection and to fix them to ocean bottom materials

- Corals live in a symbiotic relationship with algae… algae carries out photosynthesis of some of the corals food requirements… coral provides nutrients and physical protection for the algae

- coral reefs are the most diverse ecosystems of the marine environment… reef biodiversity is currently suffering from natural and anthropogenic threats

- with few exceptions corals are subtropical and inhabit warm waters on the eastern sides of continents between 30o N – 30o S; at depths 10m-55m; in waters of 27o/oo to 40o/oo salinity; and 18o C – 29o C[a few deep water and cold water species which do not utilize algae]

Coral Reef Distribution

Figure 13.15

Coral Reefs

- corals are best known as colonial animals and they are found congregated in structures that may be millions of years old

- building on the foundation of existing coral skeletons, new individuals expand the reef both horizontally and vertically

- coral reefs can take several forms:

fringing barrier atoll

Coral Reef Formation and Forms

Figure 13.16

Coral Bleaching- as the text says, for reasons that are not fully known,

some corals have begun expelling their nutrient-supplying algae in a process termed coral bleaching for the bleached white appearance that is given to coral doing this

- the “why” of it is difficult- global warming / warmer water temperature?; pollution? disease? runoff / sedimentation?;

- complicating the search for an answer is the lack of general knowledge about coral growth-and-death cycle patterns (if any should exist)

Wetlands, Salt Marshes, and Mangrove Swamps

- occupying the transition zone between land and water are the marine wetlands… regions that are periodically or permanently submerged in sea water… trapping sediments, these wetlands help build coastland and protect existing coastal areas from

storms and erosion- these are regions of significant primary productivity

from hydrophytic vegetation [water growing] and/or halophytic vegetation [salt tolerant]

- many marine species visit the submerged wetlands to feed or spawn and many utilize them as nursery areas for young

Coastal Salt Marsh

Figure 13.17

Mangroves

Figure 13.18

Human Impact on Coastal Environments

You can read for yourself.

I am not going to cover it and it is not on the exam.

Professionally, I think that the section does

not do justice to this planning issue.

Many volumes of texts and professional

publications have been

written on this issue.

Concise coverage continues to elude us.