Marine processes Flashcards
What are the four main ocean basins?
Atlantic
Arctic (shallowest)
Indian
Pacific (largest)
Describe the features of an ocean basin. Answer must describe the continental shelf.
The continental shelf is the gradually sloping end of a continent that extends under the ocean.
The ocean covering the continental shelf can be as deep as 350 m.
Large mineral, oil and natural gas deposits are found here.
At the edge of the continental shelf, the ocean floor plunges steeply 4 to 5 kilometers.
The continental slope extends from the outer edge of the continental shelf down to the ocean floor.
Conditions on continental slope vary as you go down it. Like temperature and pressure.
Features include; Oceanic shelf, oceanic slope, continental slope, seamount, oceanic trench, volcanic island, abyssal plain and mid ocean ridge.
Why is the sea salty?
Probably, the ocean was salty as soon as it formed. More salts have accumulated gradually, as more of the rocks of the crust were broken down by water (weathered).
The composition of the sea salt has been about the same for about 1 billion years. That is because a balance exists between input of salts (mainly by rivers) and output (mainly by sediments).
The early ocean, 3.8 billion years ago, was probably similar in composition to today, except for changes caused by living things. The most important of these is the production of oxygen by plants.
- 5% Water
- 5% dissolved salts (NaCl most abundant) chemicals leached from the rocks of the crust, plus some volatile chemical (hydrochloric acid and hydrogen sulfide) released from the earths interior and by volcanoes.
What is the Thermohaline circulation?
This is a deep ocean process involving sub-surface currents.
It is a density driven flow of water generated by differences in salinity or temperature. This flow is slow moving (<50km per year) as it is restricted by basin geometry.
When two water masses of differing densities come into contact, denser mass will displace and under ride the less dense water mass.
Salinity and temperature vary little once water water sinks because it is isolated from the atmosphere.
What changes is the surface waters of the ocean exposed to?
Salinity, through evaporation (more saline) or precipitation (less saline).
Temperature, through cooling or heating.
Sea ice formation is especially important
Sea ice loses heat from the ocean which can impact salinity. When water freezes it freezes freshwater making liquid water more saline.
In equatorial regions the water is warmer so more saline due to more evaporation.
Depth circulation pattern. Cold water at poles sinks, makes its way back to equator and process starts again.
Describe the worlds main currents in terms of the thermohaline water conveyor belt.
ABW: Densest deep water mass forms beneath the Arctic and flows up the Atlantic towards the equator.
Most deep water originates in the North Atlantic where surface currents merge and sink forming NADW.
NADW flows south until it mixes with the antarctic circumpolar current flowing eastward carried into the Indian and pacific ocean where it warms, rises via the gulf stream.
Describe the Mediterranean sea circulation
Surface and subsurface circulation occur because evaporation exceeds precipitation and river runoff combined.
The Atlantic ocean water flows in through the straits of Gibraltar at the surface while warm, highly saline Mediterranean sea water flows out through the Straits at the bottom. (Because freshwater is lost it becomes more saline.)
Over Gibraltar sill comes up to surface so dense salty water is trapped. Some is transferred over the sill into the Atlantic and sink down.
The Mediterranean outflow makes an important contribution to the heat and salt content of the North Atlantic.
Describe the effects of the one of the ocean surface processes - CURRENTS
Currents are mainly driven by wind.
Wind imparts frictional force on the water surface. This makes the surface water move at 3-5% of wind speed which extends to approximately 100m deep.
Main currents:
Warm equatorial currents driven west across oceans by trade winds.
At West coast of ocean deflected towards poles.
Cold water currents complete gyre along east coast of the ocean.
In Doldrum belt (3-10 degrees north) equatorial counter current flows eastwards between gyres.
2 major gyres in northern hemisphere are the gulf stream and Kuroshio.
What is the ‘Wave period’?
This is a wave classification system that takes into account the period, wavelength, wave type and the cause to classify a wave.
What are the 7 different types of wave?
Capillary wave Chop Swell Seiche Tsunami Tide Internal wave
What are the main features when describing tides?
It’s a type of wave form.
Differences in tides are caused by the interactions of the ocean, sun and moon.
Crest = high tide
Trough - low tide
Tidal range = the vertical difference between high and low tide.
Most coasts are semi-diurnal (get two tides per day)
Tidal period = time between consecutive high and low tides.
tides are delayed by 50 minutes per day.
Describe the causes of tidal range.
Tides arise from the response to complex lunar and solar interactions with the Earths Oceans.
These effects are:
gravitational attraction which pulls the ocean towards the moon and sun, creating two gravitational tidal bulges in the ocean creating high tides.
Centrifugal effect which is the push outward from the rotation about the centre mass. Centrifugal effect is due to rotation of moon but an equal but opposite force to gravitational force.
The moon exerts twice the gravitational attraction as the sun because the moon is closer to earth. Gravity varies directly with mass, but inversely with distance.
What causes changes in the tidal range?
Over a month the daily tidal ranges vary systematically with the cycle of the moon, causing spring and neap tides.
Tidal range is also altered by the shape of a basin and bathymetry.
The tides are delayed by 50 mins each day due to the earth on its axis and the moon in its orbit both revolve eastward.
Describe how two tidal bulges of water about the same size are positioned on opposite sides of the earth.
Gravitational attraction varies with distance between the masses. Water is also displaced to the side of the Earth that faces away from the moon.
The gravitational attraction and centrifugal force produce two resultant bulges of water about the same size on opposite sides of the earth.
Describe a spring tide
A spring tide occurs when the earth, moon and sun are aligned in a straight line. This constructive interference, produces high high tides and low low tides giving the biggest range of tides.
Spring tides coincide with the new moon and full moon because there is attraction to the sun and moon but the centrifugal force adds more attraction on the moon side so created a spring tide.
