Seafloor and Earth Systems
This submerged edge of a continent includes the continental shelf, slope and rise and connects the land to the deep-ocean basin.
What is the continental margin?
Wind, differences in temperature and gravity are three forces that drive these large-scale movements of surface water.
What are surface ocean currents?
This is the uninterrupted distance over which wind blows across the ocean. A greater distance generally allows larger waves to form.
What is fetch?
Waves approach a beach at an angle, moving sand along the shoreline in a repeated zigzag pattern.
What is longshore drift?
Pollution released from a wastewater pipe is this type of source, while fertiliser washed from many farms is this other type.
What are point-source and non-point-source pollution, respectively?
This broad, extremely flat part of the ocean-basin floor is usually covered by layers of fine sediment.
What is an abyssal plain?
Because its molecules are polar and form hydrogen bonds, water dissolves many substances and resists rapid temperature change. Name these two important properties.
What are water’s action as a solvent and high heat capacity?
The gravitational pull of the Moon and Sun produces this regular rise and fall of ocean water, while local currents, coastal shape and wave action influence its local expression.
What are tides?
Each year, 90,000 m³ of sand enters a beach system while 120,000 m³ leaves. Identify the sand budget and the likely coastal process.
What is a negative sand budget of 30,000 m³, causing erosion?
Match each discharge to its pollution type: untreated sewage, heated cooling water, mercury, diesel, fertiliser nitrate and insecticide.
What are organic waste, thermal pollution, heavy-metal pollution, oil pollution, nutrient pollution and pesticide pollution?
A model shows two tectonic plates separating while magma rises and forms new oceanic crust. This major bathymetric feature forms at the boundary.
What is a mid-ocean ridge?
Match the ocean layers to their rapidly changing property: temperature, salinity and density.
What are the thermocline, halocline and pycnocline, respectively?
Match the wave behaviour: bending as a wave enters shallow water, bouncing from a seawall, and spreading after passing through a breakwater opening.
What are refraction, reflection and diffraction, respectively?
After a storm removes vegetation from a dune, grasses colonise first, followed by shrubs and more complex plant communities.
What is ecological succession?
Fertiliser runoff causes rapid algal growth. When the algae die, decomposers consume oxygen and this indirect measure of pollution increases. Name the process and the measure.
What are eutrophication and biochemical oxygen demand (BOD)?
Oceanic crust bends and descends beneath another plate. Name both the deep feature formed at the boundary and the tectonic process occurring there.
What are a deep-sea trench and subduction?
Wind and Ekman transport move surface water away from a coastline. Cold, nutrient-rich water rises to replace it, generally increasing biological productivity.
What is coastal upwelling?
A wave travels from deep water towards a shallow beach. Describe what happens to its celerity, wavelength and height before it breaks.
What is decreasing celerity, shortening wavelength and increasing wave height or steepness until breaking occurs?
Aerial photographs show that beach width decreased from 60 metres in 2016 to 48 metres in 2021 and 35 metres in 2026. The dune toe also moved nine metres inland. Interpret this longitudinal evidence.
What is a continuing trend of coastal erosion and shoreline retreat? The data show the trend but do not, by themselves, prove its cause.
Site A has low nitrate and phosphate, 25 faecal-coliform CFU/100 mL, dissolved oxygen of 8.1 mg/L and BOD of 1.5 mg/L. Site B has high nutrients, 900 faecal-coliform CFU/100 mL, dissolved oxygen of 3.2 mg/L and BOD of 8.5 mg/L. Which site has poorer water quality, and what evidence supports your conclusion?
What is Site B? Direct tests show high nutrients and faecal coliform, while high BOD and low dissolved oxygen indicate substantial organic pollution.
Seawater evaporates, condenses and returns as precipitation; phytoplankton remove dissolved carbon dioxide and release oxygen; respiration reverses this gas exchange. Name the three interacting cycles.
What are the water, carbon and oxygen cycles?
Parcel A is 25°C with a salinity of 34 PSU. Parcel B is 2°C with a salinity of 35 PSU. Identify which parcel will sink, the circulation it helps drive, and why oxygen may be low beneath a stable thermocline.
What is Parcel B, because colder, saltier water is denser; it helps drive thermohaline circulation, while limited mixing and oxygen-consuming decomposition can produce an oxygen minimum zone?
Equatorial Pacific trade winds weaken, warm surface water spreads east and upwelling near South America decreases. Identify the event and predict its effects on nutrient supply and eastern Australian rainfall.
What is El Niño, producing reduced nutrient supply in the eastern Pacific and often reduced rainfall in eastern Australia?
After a groyne is installed, the beach widens by 18 metres on its updrift side but narrows by 14 metres downdrift. Nearby seagrass also experiences increased sedimentation. Evaluate the claim that the groyne “solved the erosion problem”.
What is an unsupported claim? The groyne trapped sand locally but interrupted longshore drift, transferred erosion downdrift and affected the marine ecosystem.
Following the installation of riparian buffers and constructed wetlands, turbidity and nutrients fall, seagrass expands, pollution-tolerant worms decline and the biotic-index score rises from 3 to 7. Evaluate the management strategy.
What is an effective sustainable management strategy? The improved biotic index and recovery of seagrass as a bioindicator suggest reduced siltation and nutrient pollution.