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QCAA Marine Science EA study materials
QCAA Marine Science EA study resources

QCAA Marine Science EA practice questions

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Question 1Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which property of seawater increases as salinity rises, assuming temperature is held constant?

  1. Density Correct answer.
  2. Dissolved oxygen concentration
  3. Heat capacity
  4. Transparency

Explanation

Adding dissolved salts increases the mass per unit volume of seawater, so density rises with salinity when temperature is unchanged. Oxygen solubility and heat capacity generally fall as salinity increases, and transparency is governed mainly by suspended particles and light absorption.

Question 2Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

What is the main reason surface ocean water in polar regions is denser than surface water near the equator?

  1. Stronger wind mixing
  2. Greater tidal range
  3. Lower temperature and higher salinity Correct answer.
  4. Higher nutrient concentration

Explanation

Cold polar water is close to freezing, and freezing and evaporation can concentrate salts, so both low temperature and elevated salinity raise density. Nutrients, tides and wind mixing affect biological production and currents but are not the primary density controls.

Question 3Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which process transfers heat from the ocean to the atmosphere most directly?

  1. Tidal friction along the seafloor
  2. Latent heat release during evaporation and condensation Correct answer.
  3. Downwelling of cold surface water
  4. Sedimentation of organic particles

Explanation

Evaporation removes latent heat from the ocean surface, and when that water vapour condenses in the atmosphere the heat is released, warming the air. Downwelling, tidal friction and sedimentation involve mechanical or gravitational energy rather than direct ocean-to-atmosphere heat transfer.

Question 4Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A scientist measures a seawater sample with a salinity of 35 and a temperature of 25 degrees Celsius. Which statement best describes this water?

  1. It is brackish estuarine water
  2. It is hypersaline lagoon water
  3. It is typical open-ocean surface water Correct answer.
  4. It is a cold polar water mass

Explanation

Average open-ocean salinity is about 35 and warm surface temperatures near 25 degrees Celsius are common in tropical and subtropical seas. Polar water would be much colder, estuarine water much fresher, and hypersaline lagoons would exceed normal ocean salinity.

Question 5Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

What primarily drives the large-scale surface currents of the world ocean?

  1. Hydrothermal vent discharge
  2. Prevailing winds and the Coriolis effect Correct answer.
  3. Bioluminescence of plankton
  4. Seafloor spreading rates

Explanation

Surface currents are driven mainly by prevailing winds pushing water, with the Coriolis effect deflecting the flow and basin boundaries shaping gyres. Vent discharge, seafloor spreading and plankton activity do not generate basin-scale surface circulation.

Question 6Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which factor most strongly controls the depth to which sunlight penetrates the ocean?

  1. The tidal phase
  2. Turbidity and dissolved substances in the water Correct answer.
  3. The salinity of the water
  4. The depth of the seafloor

Explanation

Light is attenuated by absorption and scattering, so suspended sediment, plankton and coloured dissolved matter strongly control the photic depth. Salinity, tidal phase and bottom depth do not directly determine how far light travels through water.

Question 7Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which of the following best describes a spring tide?

  1. A tide that occurs only in the spring season
  2. A tide with an unusually small range near the quarter moons
  3. A tide caused solely by local wind setup
  4. A tide with an unusually large range near new or full moon Correct answer.

Explanation

Spring tides occur when the Sun and Moon align, at new and full moon, so their tidal forces reinforce each other and produce the largest tidal range. They are not tied to the season, and neap tides occur near the quarter moons.

Question 8Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which zone of the ocean is characterised by the greatest pressure and complete absence of sunlight?

  1. The abyssal and hadal depths Correct answer.
  2. The surface mixed layer
  3. The intertidal zone
  4. The coastal surf zone

Explanation

Pressure increases with depth, and sunlight is essentially absent below about one thousand metres, so the abyssal and hadal realms experience the highest pressures and total darkness. Intertidal, surface and surf zones are shallow, well lit and low pressure.

Question 9Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A coastal bay receives freshwater runoff and has restricted exchange with the open sea. What is the most likely effect on its surface salinity?

  1. It decreases relative to the adjacent ocean Correct answer.
  2. It remains identical to the open ocean
  3. It increases sharply
  4. It becomes hypersaline

Explanation

Freshwater input dilutes the surface layer faster than restricted exchange can replace it, so surface salinity falls below open-ocean values. Salinity would rise only if evaporation greatly exceeded freshwater input in a poorly flushed basin.

Question 10Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Why does the Coriolis effect deflect moving water to the right in the Northern Hemisphere?

  1. Gravity is stronger in the Northern Hemisphere
  2. The Moon orbits closer to the Northern Hemisphere
  3. Earth rotates eastward, so the surface moves faster at lower latitudes Correct answer.
  4. Seawater is denser north of the equator

Explanation

Because Earth rotates, points near the equator travel eastward faster than points near the poles, so a moving parcel conserves angular momentum and appears deflected relative to the rotating frame. The deflection is an apparent force arising from rotation, not from gravity, lunar distance or density differences.

Question 11Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

In a two-layer estuary, why does the denser seawater tend to move inland along the bottom?

  1. Saltwater intrusion driven by density differences Correct answer.
  2. River flow drags seawater upstream
  3. Tidal bores carry seawater inland only
  4. Wind pushes the seawater inland

Explanation

Seawater is denser than fresh river water, so it forms a wedge that moves landward along the bottom beneath the outflowing freshwater. Wind and river flow act against inland seawater movement, and tidal bores are a special localised feature.

Question 12Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

What happens to a parcel of surface water when it is cooled at high latitude and becomes denser than the water beneath it?

  1. It evaporates rapidly
  2. It sinks and contributes to deep-water formation Correct answer.
  3. It expands and floats away
  4. It becomes less saline

Explanation

When surface water cools and becomes denser than underlying water, it sinks, a process that forms dense deep water masses at high latitudes. Sinking does not cause evaporation or freshening, and cooling makes water contract rather than expand.

Question 13Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which combination best explains why tropical surface waters are typically low in nutrients?

  1. High salinity removes nutrients
  2. Strong stratification limits upward nutrient supply Correct answer.
  3. Upwelling is strongest at low latitudes
  4. Cold water prevents nutrient dissolution

Explanation

Warm surface water forms a stable, strongly stratified layer that suppresses vertical mixing, so nutrients regenerated at depth are not readily returned to the surface. Nutrient supply is not controlled by cold dissolution, salinity, or strong low-latitude upwelling, which is actually limited in many tropical gyres.

Question 14Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A ship measures water temperature falling sharply between 200 and 1000 metres depth. What feature is being crossed?

  1. The pycnocline
  2. The halocline
  3. The photic zone
  4. The thermocline Correct answer.

Explanation

A rapid decrease in temperature with depth marks the thermocline, the transition layer between warm surface water and cold deep water. A halocline is a salinity gradient, a pycnocline is a density gradient, and the photic zone refers to light penetration.

Question 15Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which process is most important for bringing nutrient-rich deep water to the surface along a western continental coast?

  1. Bioluminescence
  2. Tidal mixing
  3. River discharge
  4. Wind-driven coastal upwelling Correct answer.

Explanation

Along coasts where winds blow surface water offshore, Ekman transport moves water away from the coast and deeper nutrient-rich water rises to replace it. Tidal mixing, river discharge and bioluminescence do not systematically lift deep water in this way.

Question 16Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

How does the presence of sea ice affect the salinity of the underlying surface water during freezing?

  1. Salinity is unchanged because ice is frozen seawater
  2. Salinity increases as salts are excluded from the ice Correct answer.
  3. Salinity becomes zero beneath the ice
  4. Salinity decreases because ice adds freshwater

Explanation

When seawater freezes, much of the dissolved salt is expelled as brine, so the remaining liquid water becomes more saline. Ice formation therefore raises the salinity of the underlying water rather than freshening it or leaving it unchanged.

Question 17Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A tsunami generated by a submarine earthquake is travelling across the open ocean. Which statement best describes its behaviour?

  1. Negligible energy until it reaches shore
  2. Very slow speed in deep water
  3. Short wavelength and high amplitude in deep water
  4. Long wavelength and low amplitude in deep water Correct answer.

Explanation

In the deep ocean a tsunami has a very long wavelength and small amplitude, allowing it to travel fast with little visible change at the surface. As it approaches shallower water it slows, the wavelength shortens and amplitude grows, causing destructive run-up.

Question 18Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which factor would most increase the tidal range at a coastal location?

  1. A funnel-shaped estuary that amplifies the incoming tide Correct answer.
  2. A small tidal prism
  3. A wide open coast with deep offshore water
  4. A coastline aligned parallel to tidal flow

Explanation

A narrowing, funnel-shaped estuary constricts the incoming tidal wave, raising its height and increasing the tidal range. Open coasts, aligned shorelines and small tidal prisms tend to reduce amplification.

Question 19Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Why does the ocean's surface mixed layer generally have a lower density than the deep water beneath it?

  1. It is warmer and often fresher than deep water Correct answer.
  2. It has more suspended sediment
  3. It contains more dissolved salts
  4. It experiences higher pressure

Explanation

Surface water is warmed by solar radiation and receives freshwater from rain and runoff, both of which lower density, so it floats above denser deep water. Higher salinity, pressure and sediment content would not explain the lower surface density.

Question 20Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A deep-ocean water mass has formed near Antarctica and is traced northward at depth. Which property change would you expect as it travels?

  1. Rapid cooling and increased salinity
  2. Conversion to freshwater
  3. Gradual warming and slight freshening through mixing Correct answer.
  4. Complete loss of dissolved oxygen

Explanation

A deep water mass slowly mixes with surrounding water as it travels, so it warms slightly and may freshen as it exchanges properties with adjacent water masses. It does not cool further, lose all oxygen, or become freshwater.

Question 21Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Two adjacent coastal sites have the same wind speed, but one has a much larger fetch. Which site is likely to develop larger wind waves, and why?

  1. Neither, because wind speed alone determines wave height
  2. The site with smaller fetch, because waves are steeper
  3. The site with smaller fetch, because of stronger refraction
  4. The site with larger fetch, because wind acts over a longer distance Correct answer.

Explanation

Wave growth depends on wind speed, duration and fetch, so a longer fetch allows the wind to transfer more energy to the waves and build larger waves. Fetch does not make waves steeper or stronger at shorter distances, and wave height is not determined by wind speed alone.

Question 22Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A scientist observes that a coastal upwelling event coincides with a bloom of phytoplankton. Which explanation best links these observations?

  1. Upwelling removes predators
  2. Upwelling delivers nutrients that relieve nutrient limitation Correct answer.
  3. Upwelling warms the surface water
  4. Upwelling increases salinity

Explanation

Deep water is rich in nutrients such as nitrate and phosphate, so upwelling relieves the nutrient limitation that normally constrains phytoplankton growth and can trigger a bloom. Upwelling typically cools the surface, does not remove predators, and has little direct effect on salinity.

Question 23Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Why does the ocean's biological pump contribute to the vertical gradient of dissolved carbon?

  1. Organic carbon sinks and is respired at depth Correct answer.
  2. Deep water is warmer than surface water
  3. Surface water releases carbon to the atmosphere
  4. Carbon dioxide dissolves more readily at depth

Explanation

Photosynthesis fixes carbon in surface waters, and sinking organic matter carries it downward where respiration releases dissolved carbon at depth, creating higher deep-ocean carbon concentrations. Carbon dioxide is more soluble in cold water, but the biological pump specifically depends on sinking and respiration, and deep water is colder, not warmer.

Question 24Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A coastline experiences a large storm surge. Which combination of factors most likely produced the highest surge?

  1. High atmospheric pressure and offshore winds
  2. Low atmospheric pressure and strong onshore winds Correct answer.
  3. Spring tide and offshore winds
  4. Cold water and weak winds

Explanation

Storm surge results from low atmospheric pressure allowing the sea surface to rise and from strong onshore winds piling water against the coast, so both together produce the greatest surge. High pressure, offshore winds and weak winds all act to reduce surge height.

Question 25Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which statement best explains why the deep ocean is generally cold even at low latitudes?

  1. Deep currents are driven by tides alone
  2. Deep water is cooled by hydrothermal vents
  3. Dense cold water forms at high latitudes and flows along the seafloor Correct answer.
  4. Sunlight cannot penetrate deep water

Explanation

Cold, dense water forms at high latitudes and sinks, then spreads along the seafloor toward lower latitudes, so the deep ocean remains cold everywhere. Lack of sunlight is a consequence rather than the cause, hydrothermal vents are localised, and tides alone do not drive the deep circulation.

Question 26Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which property of seawater increases as both temperature and salinity increase?

  1. Compressibility
  2. Density Correct answer.
  3. Alkalinity
  4. Viscosity

Explanation

Density is controlled mainly by temperature and salinity; colder and saltier water is denser, while warming and freshening reduce it. Viscosity and compressibility change with temperature and pressure but are not defined by salinity in this way, and alkalinity is a chemical acid-neutralising capacity.

Question 27Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Approximately what proportion of dissolved salts in seawater is accounted for by sodium and chloride ions combined?

  1. About 25 percent
  2. About 10 percent
  3. More than 85 percent Correct answer.
  4. About 50 percent

Explanation

Sodium and chloride are by far the dominant ions in seawater, together making up the large majority of dissolved salt by mass. The remaining mass comes from ions such as magnesium, sulfate, calcium and potassium, which are present in much smaller amounts.

Question 28Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A scientist measures salinity at several depths in the open ocean and finds values of about 35 throughout. What does this indicate about the water column?

  1. The water is uniformly dense at all depths
  2. Salinity is roughly conservative with depth at this location Correct answer.
  3. Evaporation exceeds precipitation across the whole column
  4. The water column is strongly stratified by salinity

Explanation

Salinity is a conservative property, meaning it changes only through processes such as mixing, evaporation, precipitation and freshwater input. A near-constant profile shows no strong salinity-driven layering at that site, although density may still vary because of temperature.

Question 29Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

What is the main reason that seawater freezes at a lower temperature than fresh water?

  1. Seawater is less dense than fresh water at all temperatures
  2. Seawater has a much higher heat capacity than fresh water
  3. Dissolved salts interfere with the formation of the ice crystal lattice Correct answer.
  4. Seawater contains more dissolved gases than fresh water

Explanation

Freezing requires water molecules to arrange into an ordered crystal lattice. Dissolved ions disrupt this ordering, so more energy must be removed before ice forms, lowering the freezing point. This is a colligative effect that depends on the amount of dissolved material.

Question 30Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which statement correctly describes the general pattern of surface ocean temperature from the equator toward the poles?

  1. It stays constant because solar heating is absorbed evenly
  2. It increases poleward because cold water sinks and is replaced
  3. It decreases poleward as solar heating per unit area declines Correct answer.
  4. It rises and falls with longitude rather than with latitude

Explanation

Solar radiation strikes the tropics more directly, concentrating energy per unit area, while higher latitudes receive the same energy spread over a larger area and at a lower angle. This produces warm tropical surface water and progressively cooler water toward the poles, modified by currents.

Question 31Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which force drives the large-scale horizontal movement of surface ocean water in response to wind?

  1. Wind stress acting on the sea surface Correct answer.
  2. Coriolis force
  3. Tidal force
  4. Pressure gradient force

Explanation

Wind transfers momentum to the sea surface through friction, and this stress sets surface water in motion. The Coriolis force and pressure gradients then shape the resulting flow direction and geostrophic balance, but they do not initiate it.

Question 32Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which feature forms where a river delivers sediment to a coast with weak wave energy and gentle currents?

  1. A submarine canyon
  2. A barrier reef
  3. An abyssal plain
  4. A river delta Correct answer.

Explanation

When a river's sediment supply exceeds the ability of waves and currents to remove it, sediment accumulates at the mouth and builds a delta. Weak wave energy allows deposition rather than erosion, so the sediment deposit persists and progrades seaward.

Question 33Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

What is the primary cause of the daily rise and fall of tides at most coastlines?

  1. Submarine volcanic activity
  2. Seasonal changes in wind strength
  3. The gravitational pull of the Moon and Sun on the ocean Correct answer.
  4. Variations in seawater density

Explanation

Tides arise mainly from the gravitational attraction of the Moon and, to a lesser extent, the Sun, combined with the orbital motion of the Earth-Moon system. These forces produce bulges of water that coastlines rotate through each day.

Question 34Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A parcel of seawater at 10 degrees Celsius is warmed to 20 degrees Celsius while its salinity stays constant. What happens to its density and its volume?

  1. Density decreases and volume increases slightly Correct answer.
  2. Density increases and volume decreases
  3. Density decreases and volume decreases
  4. Density and volume both remain unchanged

Explanation

Warming increases the kinetic energy of water molecules, so they occupy slightly more space and the volume expands. Because the same mass now fills a larger volume, density falls; this thermal expansion is a key reason warm surface water floats above cold water.

Question 35Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A coastal location experiences two high tides each day that are of unequal height. Which term best describes this tidal pattern?

  1. Spring tide
  2. Mixed semidiurnal tide Correct answer.
  3. Neap tide
  4. Diurnal tide

Explanation

A mixed semidiurnal pattern has two high and two low tides per day, with successive highs of noticeably different heights. Diurnal tides have one high and one low per day, while spring and neap describe the size of the tidal range rather than its daily pattern.

Question 36Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Why does a tidal bore sometimes form in a funnel-shaped estuary?

  1. The rising tide advances into a narrowing channel faster than the water ahead can retreat Correct answer.
  2. The incoming tide is funnelled and slowed by the widening channel
  3. The estuary floor is perfectly flat and featureless
  4. Freshwater outflow always exceeds the tidal inflow

Explanation

In a narrowing estuary, the incoming tide is compressed into a smaller cross-section, so the flood front steepens and can overtake the outgoing river water. This produces a travelling step or bore rather than a gradual rise. A widening channel would spread the tide and flatten it.

Question 37Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which statement best explains why the open-ocean thermocline is generally sharper in tropical regions than at high latitudes?

  1. High-latitude waters are heated more strongly, which sharpens the density gradient
  2. Tropical waters receive strong heating that maintains a warm, light surface layer over cold deep water Correct answer.
  3. Deep water is warmer in the tropics, increasing the contrast
  4. Tropical regions lack any wind mixing, so the gradient stays sharp

Explanation

Strong tropical solar heating maintains a warm, buoyant surface layer, while deep water remains cold, creating a large density contrast over a short depth interval. At high latitudes, surface cooling and mixing reduce the temperature contrast, so the thermocline is weaker and deeper.

Question 38Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A scientist tracks a subsurface water mass and finds it has low oxygen and high nutrient concentrations. What does this most likely indicate?

  1. The water mass is very young and recently ventilated
  2. The water mass is currently being strongly mixed by winter storms
  3. The water mass has been isolated from the atmosphere for a long time Correct answer.
  4. The water mass has recently formed at the surface

Explanation

Oxygen enters deep water mainly at the surface during formation and is consumed by respiration as the water travels. Long isolation from the atmosphere allows oxygen to be depleted while respired nutrients accumulate, producing the low-oxygen, high-nutrient signature.

Question 39Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

How does the Ekman transport of surface water in the Southern Hemisphere compare with the wind direction?

  1. Surface water moves directly upwind
  2. Surface water moves directly downwind
  3. Surface water moves about 90 degrees to the right of the wind
  4. Surface water moves about 90 degrees to the left of the wind Correct answer.

Explanation

Ekman transport describes the net movement of the wind-driven surface layer, which is deflected about 90 degrees from the wind because the deflection accumulates with depth. In the Southern Hemisphere, the Coriolis deflection is to the left, so the net transport is left of the wind.

Question 40Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which condition would most favour the formation of dense, oxygen-rich deep water?

  1. Warm, fresh surface water in a low-latitude sea
  2. Warm, salty surface water in an enclosed basin
  3. Cold, salty surface water exposed to strong cooling and wind mixing Correct answer.
  4. Fresh surface water capped by a strong halocline

Explanation

Deep water forms when surface water becomes dense enough to sink. Cooling and high salinity both raise density, and wind mixing helps the dense water mass grow and carry dissolved oxygen downward. Low-latitude warm water is too buoyant to sink in this way.

Question 41Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A long swell generated by a distant storm arrives at a coast. Why does it typically have a longer period than locally generated wind waves?

  1. Shorter waves are absorbed by the storm before they can leave
  2. The swell gains energy as it crosses the ocean
  3. Longer waves travel faster and outrun shorter waves, so they arrive first Correct answer.
  4. Local winds slow the shorter waves so they arrive later

Explanation

In deep water, wave speed increases with wavelength, so long-period swell outpaces the shorter, slower waves generated in the same storm. The short waves dissipate or remain behind, leaving the long-period swell to dominate at distant coasts.

Question 42Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Which process transfers heat from the ocean to the atmosphere most effectively during a cold-air outbreak over warm water?

  1. Conduction through the seafloor
  2. Absorption of longwave radiation by the sea surface
  3. Evaporation followed by condensation, plus direct sensible heating Correct answer.
  4. Release of latent heat by freezing seawater

Explanation

When cold air passes over warmer water, the ocean loses heat both as sensible heat by conduction and as latent heat through evaporation, which later condenses in the atmosphere. These turbulent fluxes are far larger than the other processes listed during such an event.

Question 43Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A narrow, steep-sided submarine canyon cuts across the continental shelf and slope. Which statement best explains its formation?

  1. Growth of coral frameworks along the shelf edge
  2. Repeated erosion by sediment-laden density flows moving downslope Correct answer.
  3. Wind-driven wave erosion during storms
  4. Slow accumulation of fine sediment over millions of years

Explanation

Submarine canyons are eroded by turbidity currents and other sediment gravity flows that travel downslope and scour the seabed. These flows can cut deeply into the shelf and slope over time, maintaining steep canyon walls.

Question 44Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A beach profile shows sand being removed from the upper beach during winter storms and returning during calm summer periods. What does this demonstrate?

  1. Longshore drift has stopped entirely
  2. The beach is in long-term erosion with no recovery
  3. Sediment is permanently lost to the deep ocean each winter
  4. The beach profile adjusts seasonally to wave energy Correct answer.

Explanation

High-energy winter waves move sand offshore into bars, flattening the profile, while gentler summer waves move it back onshore. This seasonal exchange shows that the beach profile adjusts to wave conditions rather than being permanently lost.

Question 45Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Why does the sea surface slope gently upward away from a persistent low-pressure weather system?

  1. Low pressure causes the seafloor to rise
  2. Coriolis deflection raises sea level directly beneath the low
  3. Seawater becomes denser under low pressure and expands
  4. The reduced atmospheric pressure allows the sea surface to rise slightly, and winds pile water toward the centre Correct answer.

Explanation

A lower atmospheric pressure exerts less downward force on the sea surface, so the water rises by roughly one centimetre per hectopascal of pressure deficit. Converging winds around the low also push water toward the centre, adding to the effect.

Question 46Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A water mass formed in the North Atlantic is traced southward at depth. Which combination of changes would you expect as it travels?

  1. Oxygen increases and nutrients decrease
  2. Oxygen decreases and nutrients increase Correct answer.
  3. Temperature increases and salinity increases sharply
  4. Density decreases and the water rises to the surface

Explanation

Once isolated from the surface, deep water cannot take up new oxygen, and respiration by organisms consumes the oxygen present. The same respiration releases nutrients, so oxygen falls and nutrients accumulate along the flow path.

Question 47Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A coastal upwelling region shows high surface productivity despite being at a low latitude. Which explanation best accounts for this?

  1. Deep water rich in nutrients is brought to the sunlit surface Correct answer.
  2. Surface heating concentrates nutrients by evaporation
  3. Rainfall delivers nutrients directly to the surface layer
  4. Warm surface water holds more dissolved oxygen, stimulating growth

Explanation

Upwelling lifts cold, nutrient-rich water from depth into the euphotic zone, where light is sufficient for photosynthesis. The combination of abundant nutrients and sunlight supports large phytoplankton blooms even where surface water would otherwise be nutrient-poor.

Question 48Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

Two water masses meet at a front: one is cold and salty, the other warm and fresh. Which outcome is most likely if they have similar densities?

  1. The warm fresh water sinks rapidly beneath the cold salty water
  2. Both masses immediately freeze at the boundary
  3. The two masses mix along a sloping density surface with little vertical exchange Correct answer.
  4. The cold salty water floats above the warm fresh water

Explanation

When water masses of similar density meet, the boundary between them tends to slope rather than overturn, so they mix mainly sideways along the density surface. This produces a front with limited vertical exchange, often visible as a sharp change in temperature and colour.

Question 49Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

A scientist compares two marginal seas at the same latitude: one is nearly enclosed by land, the other is open to the ocean. Which difference in salinity is most likely, and why?

  1. Both seas must have identical salinity at the same latitude
  2. The open sea is saltier because it has no river input
  3. The enclosed sea is fresher because it receives more rainfall
  4. The enclosed sea is saltier because evaporation exceeds freshwater input and exchange is restricted Correct answer.

Explanation

In a restricted basin where evaporation removes more water than rivers and rain supply, dissolved salts become concentrated because exchange with the open ocean is limited. An open sea mixes freely with the wider ocean, so its salinity stays closer to the global average.

Question 50Marine systems and the ocean environment (oceanography, water properties, coastal and deep-ocean processes)

During a strong El Nino event, what change in upwelling is typically observed along the eastern equatorial Pacific?

  1. Upwelling shifts to the western Pacific without any change in winds
  2. Upwelling stops entirely and the thermocline vanishes
  3. Upwelling weakens as trade winds slacken and the thermocline deepens in the east Correct answer.
  4. Upwelling strengthens because trade winds increase

Explanation

El Nino involves weakened trade winds, which allow warm surface water to spread eastward and depress the thermocline in the eastern Pacific. With a deeper thermocline, upwelling brings warmer, nutrient-poorer water, reducing productivity.