Chapter 16: The Oceans, Coastal Processes, and Landforms

Chemical Composition of Seawater

- Water 'universal solvent'seawater is a solution - Ocean chemistry: f(x) of interchange btw seawater, atmosphere, minerals, bottom sediments and biota - 99% of dissolved solids comprised of 7 elements (Cl, Na, Mg, SO4, Ca, K, Br)

➢ Coral Bleaching

• Occurs as normally colorful corals turn stark white • Expelling their own nutrient-supplying algae • Without algae, corals die • Now occurring at an unprecedented rate • Average ocean temperatures climb higher • End of 2000, 30% of reefs were lost • 2010, most rapid and severe coral bleaching and mortality events on record • Aceh, Indonesia species declined 80% in a few months

➢ Tides

• Pattern of twice-daily oscillations in sea level produced by astronomical relations among the Sun, the Moon, and Earth • Experienced in varying degrees around the world

➢ Breaker

• Point where a wave's height exceeds its vertical stability • Wave breaks as it approaches the shore

➢ Swells

• Regular patterns of smooth, rounded waves in open water • Can range from small ripples to very large waves

➢ Flood tides

• Rising tide during the daily tidal cycle

Salinity

• Sea water is a solution, and the concentration of dissolved solids • Concentration of natural elements and compounds dissolved in solution, as solutes • Measured by weight in parts per thousand in seawater • salinity: [dissolved solids] by volume = 35‰ > concentration varies f(x) of fH20 flows and atmospheric conditions • • sub-tropical (36%o) vs. equatorial (34.5 ‰) • • brine: > 35‰; brackish <35‰ • • e.g. Red Sea 225‰; Gulf of Bothnia 25‰; Sargasso Sea 38‰

➢ Brine

• Seawater with salinity of more than 35% • Ex: the Persian Gulf

➢ Tsunami

• Seismic sea wave travelling a high speeds across the ocean • Formed by sudden motion in the seafloor • Such as sea-floor earthquake, submarine landslide, or eruption of an undersea volcano

➢ Coral

• Simple marine animal with small, cylindrical, saclike body called a polyp and exist as both solitary and colonial formations • Related to other marine invertebrates (anemones and jellyfish) • Secrete calcium carbonate (CaCO3) from lower half of their bodies • Forming a hard, calcified external skeleton

➢ Waves

• Undulation of ocean water produced by the conversion of solar energy to wind energy and then to waver energy • Energy produced in a generating region or a stormy area of the sea

➢ Neap tides

• Unusually low tidal range • Produced during the first and third quarters of the Moon, with an offsetting pull from the Sun

➢ Mangrove swamps

• Wetland ecosystem between 30 degrees N and 30 degrees S • Tends to form a distinctive community of mangrove plants

➢ Salt marshes

• Wetland ecosystem characteristic of latitudes poleward of the 30th parallel

• Physical Structure of the Ocean

• surface: mixing zone (2% of volume); well-mixed • thermocline: transition zone, 1 km thick with steep temperature gradient, little mixing (18%) • cold zone: uniform salinity/temperature values, ~0oC (doesn't freeze due to salinity and pressure), at surface H20 freezes at ~ 2oC (80%)

• Physical Structure of the Ocean

➢ Layered ➢ Four key aspects - each varies with increasing depth • Average Temperature • Salinity • Dissolved carbon dioxide • Dissolved oxygen ➢ Surface layer is warmed by the Sun and is wind driven ➢ Variations in water temperature and solutes are blended rapidly in the mixing zone • Represents only 2% of the oceanic mass ➢ Below mixing zone is the thermocline transition zone • Region more than 1 km deep of decreasing temperature gradient that lacks the motion of the surface ➢ Deep cold zone temperatures are near 0 degrees C • Seawater freezes at about -2 degrees C

• The Coastal Environment and Sea Level

➢ Littoral zone • Specific coastal environment • Region between the high-water line during a storm and a depth at which storm waves are unable to move sea-floor sediments ➢ Mean sea level (MSL) • Average of tidal levels recorded hourly at a given site over a long period • Must be at least a full lunar tidal cycle

• Inputs to the Coastal System

➢ Solar Energy • Drives the atmosphere and the hydrosphere • Conversion of insolation to kinetic energy • Produces prevailing winds, weather systems, and climate ➢ Atmospheric winds • Generate ocean currents and waves • Key inputs to the coastal environment ➢ Climatic regimes • Result from insolation and moisture • Strongly influence coastal geomorphic processes ➢ Nature of coastal rock and coastal geomorphology • Important in determining rates of erosion and sediment production ➢ Human activities • Increasingly significant input to coastal change

➢ Lagoon

• Area of coastal seawater that is virtually cut off from the ocean by a bay barrier or barrier beach • The water surrounded and enclosed by an atoll

➢ Wave refraction

• Bending process that concentrates wave energy on headlands and disperses it in coves and bays • Long term result is coastal straightening

➢ Longshore current

• Current that forms parallel to a beach as waves arrive at an angle to the shore • Generated in the surf zone by wave action, transporting large amounts of sand and sediment

➢ Barrier spit

• Depositional landform • Develops when transported sand or gravel in a barrier breach or island is deposited in long ridges that are attached at one end to the mainland partially cross the mouth of the bay

➢ Brackish

• Descriptive of seawater with salinity of less than 35% • Ex: the Baltic Sea

➢ Bay barrier

• Extensive barrier spit of sand or gravel that encloses a bay • Cuts it off completely from the ocean forming a lagoon • Produced by littoral drift and wave action • Sometimes referred to as baymouth bar

➢ Ebb tides

• Falling or lowering tide during the daily tidal cycle

➢ Wave-cut platform

• Flat or gently sloping, table-like bedrock surface • Develops in the tidal zone where wave action cuts a bench that extends from the cliff base out into the sea

➢ Coral Reefs

• Form through many generations when live corals near the ocean's surface build on the foundation of older coral skeletons • May rest upon a volcanic seamount or some other submarine feature built up from the ocean floor • Coral reef - biologically derived sedimentary rock that can assume one of several distinctive shapes • Different reef stages • Fringing reefs - platforms of surrounding coral rock • Barrier reefs - reefs that enclose lagoons • Atolls - circular, ring-shaped reefs

➢ Barrier islands

• Generally, a broadened barrier beach offshore

➢ Spring tides

• Highest tidal range • Occurs when the Moon and the Sun are in conjunction (at new Moon) or in opposition (at full Moon) stages

➢ Tombolo

• Landform created when coastal sand deposits connect the shoreline with an offshore island outcrop or sea stack

➢ Beach drift

• Material, such as sand, gravel, and shells that is moved by the longshore current in the effective direction of the waves

➢ Barrier beaches

• Narrow, long, depositional feature, generally composed of sand • Forms offshore roughly parallel to the coast • May appear as barrier islands and long chains of barrier beaches

➢ Wetlands

• Narrow, vegetated strip occupying many coastal areas and estuaries worldwide • Highly productive ecosystem • Ability to trap organic matter, nutrients, and sediment

Inputs to the Coastal System

Coastal System • coastlines>dynamic equilibrium btw wave energy, tides, wind, currents, sediment supply, slope of coastal plain, sea-level fluctuations • inputs: - solar energy (hydrosphere and atmosphere)>climate and weather - winds>ocean currents and waves - climate regimescoastal geomorphology (ppt) - coastal geology>erosion/sediment production - human activities • The Coastal Environment and Sea Level