CSS Geography Oceanography Syllabus

What factors decrease ocean surface salinity?

High precipitation, large river/freshwater inflow, melting of ice, and low evaporation.

Why is salinity highest in the subtropics (around 20°–30° latitude) rather than at the equator?

The subtropics have high evaporation and low rainfall under descending dry air, raising salinity; the equator has heavy rainfall and high humidity that dilute surface waters.

Which water body has the highest salinity, and roughly what value?

Among open seas, the Red Sea is very high (~40‰); enclosed water bodies are higher still—the Dead Sea reaches around 240‰ and the Great Salt Lake even more (these are lakes, not open ocean).

What are the two most abundant ions in seawater, and roughly what proportion of dissolved salts do they form?

Chloride (Cl⁻) and sodium (Na⁺); together as sodium chloride they make up about 85% of the dissolved salts in seawater.

What is the principle of 'constancy of composition' (Forchhammer's/Marcet's principle) for seawater?

Although total salinity varies from place to place, the relative proportions of the major dissolved ions remain almost constant throughout the world ocean.

What is the ocean (Earth's) heat budget concept?

The balance between heat gained by the ocean (mainly incoming solar radiation) and heat lost (by back radiation, evaporation, and conduction); globally averaged, gains and losses balance, but there is a surplus in the tropics and a deficit at the poles.

How is the tropical heat surplus and polar heat deficit balanced in the ocean?

By poleward heat transport via ocean currents (and the atmosphere); warm currents carry heat toward the poles and cold currents return cooler water toward the equator, maintaining overall balance.

What is the ocean's salt budget?

The balance between salt added to the ocean (river input, volcanic/hydrothermal and atmospheric sources) and salt removed (sediment deposition, sea spray, biological uptake, evaporite formation); over geological time inputs and outputs are roughly balanced, keeping mean salinity stable.

What are the three main genetic categories of ocean-floor (marine) deposits?

Terrigenous (land-derived), pelagic/biogenous (organic ooze), and authigenic/inorganic deposits (including volcanic and cosmic material).

What are terrigenous deposits?

Sediments derived from the land—sand, silt, mud (clay)—brought by rivers, wind, ice and waves, deposited mainly on continental shelves, slopes and rises.

Define pelagic oozes and their two main types.

Fine deep-sea deposits made of microscopic organism remains. Calcareous oozes (e.g., Globigerina, pteropod) form from CaCO₃ shells; siliceous oozes (e.g., diatom, radiolarian) form from silica skeletons.

What is red clay (abyssal/pelagic clay) and where is it found?

An extremely fine, reddish-brown inorganic deposit of windblown dust, volcanic and cosmic particles, found in the deepest parts of the ocean (below the carbonate compensation depth) where ooze cannot accumulate.

What is the Carbonate Compensation Depth (CCD)?

The depth (roughly 4,000–5,000 m) below which the rate of calcium carbonate dissolution exceeds its supply, so calcareous oozes do not accumulate and red clay or siliceous ooze dominates.

What drives the surface (wind-driven) circulation of the oceans?

Prevailing winds (trades, westerlies), modified by the Coriolis force, the shape of ocean basins, and density differences—producing large rotating gyres.

In which direction do the major ocean gyres rotate in each hemisphere, and why?

Clockwise in the Northern Hemisphere and anticlockwise (counterclockwise) in the Southern Hemisphere, due to the deflection of the Coriolis force.

What is thermohaline circulation (the 'global ocean conveyor belt')?

Deep, density-driven circulation caused by differences in temperature (thermo) and salinity (haline); cold, salty dense water sinks in polar regions (e.g., North Atlantic) and slowly circulates worldwide, returning as upwelled surface water.

What is upwelling and why is it important?

The rising of cold, nutrient-rich deep water to the surface (often along coasts where winds push surface water away); it supports highly productive fisheries (e.g., off Peru).

Name a major warm current and a major cold current of the North Atlantic.

Warm: the Gulf Stream / North Atlantic Drift. Cold: the Labrador Current (and the Canary Current as a cool eastern-boundary current).

What is the difference between a wave's motion and a current's motion?

In a wave the water particles move in nearly circular orbits and largely return to position, transmitting energy (not water) forward; in a current there is actual horizontal transport of the water mass over long distances.

Define wavelength, wave height, and wave period for ocean waves.

Wavelength is the horizontal distance between two successive crests; wave height is the vertical distance between crest and trough; wave period is the time taken for two successive crests to pass a fixed point.

What generates wind waves, and what three factors control their size?

Wind blowing over the sea surface generates them; their size depends on wind speed, wind duration, and fetch (the distance of open water over which the wind blows).

What is a tsunami and what usually causes it?

A series of very long-wavelength, fast-moving sea waves usually caused by sudden displacement of the seafloor—submarine earthquakes, volcanic eruptions or landslides; they are low in the open ocean but rise to great heights near the coast.

What causes ocean tides?

The gravitational attraction of the Moon (dominant) and the Sun on the Earth's water, combined with the centrifugal force of the Earth–Moon system, producing two tidal bulges that move around the Earth.

Distinguish spring tides from neap tides.

Spring tides are the highest high and lowest low tides, occurring at new and full moon when Sun, Moon and Earth are aligned (forces add). Neap tides are the lowest range, occurring at the first and third quarter when Sun and Moon are at right angles (forces partly cancel).

What is the difference between a diurnal and a semi-diurnal tide?

A diurnal tide has one high and one low tide per day; a semi-diurnal tide has two highs and two lows of roughly equal height per day. A mixed tide has two unequal highs and lows.

Give the three main categories of ocean resources mentioned in oceanography.

Biotic (living—fish, marine organisms), mineral (e.g., polymetallic/manganese nodules, salt, petroleum, sand and gravel, placer deposits), and energy resources (tidal, wave, OTEC, offshore oil and gas).

What are polymetallic (manganese) nodules?

Potato-sized concretions on the deep abyssal floor rich in manganese, iron, nickel, copper and cobalt, considered an important future mineral resource.

What is OTEC and the principle behind it?

Ocean Thermal Energy Conversion—generating power from the temperature difference between warm surface water and cold deep water; it works best in the tropics where the surface–deep temperature contrast is largest (about 20°C).

What conditions are required for the growth of coral reefs?

Warm water (about 20–25°C+), shallow depth with sunlight penetration, clear sediment-free salt water of normal salinity, and a firm substrate—conditions met mainly in tropical seas between about 30°N and 30°S.

Name the three main types of coral reef in Darwin's classification.

Fringing reefs (attached to the shore), barrier reefs (separated from the shore by a lagoon, e.g., the Great Barrier Reef), and atolls (ring-shaped reefs enclosing a central lagoon).

What is coral bleaching and what mainly causes it?

The whitening of corals when stressed corals expel their symbiotic zooxanthellae algae, losing colour and their food source. It is caused mainly by rising sea temperatures (thermal stress), and also by pollution, acidification and excess light; prolonged bleaching can kill the coral.

What are the two main causes of present-day global sea-level rise?

Thermal expansion of warming ocean water and the addition of meltwater from melting glaciers and ice sheets (e.g., Greenland and Antarctica).

Distinguish eustatic from isostatic sea-level change.

Eustatic change is a worldwide change in the actual volume/level of ocean water (e.g., from ice melting or thermal expansion). Isostatic change is a local change in land level relative to the sea (e.g., crustal uplift after deglaciation), so the sea appears to fall or rise locally.