Paper 1: oceans and coastal margins

What is the case study for a tropical storm?

Hurricane Ian (September 28th 2022)

What are some stats for hurricane Ian?

• Category 4 storm (max 155mph)

• 2nd deadliest tropical storm to strike the USA this century, killing 157 people (including in Cuba)

• Value of losses was over 50B dollars

• There was a 4.6m storm surge

• Around 10,000 people had to stay in emergency shelters as homes were destroyed

• 2000 flights cancelled on 28/09 alone

• Mosquitoes breed in excess standing water so diseases spread rapidly

How do tides affect coastal erosion?

• More sediment is eroded at the “spring tide“ ie. new moon or full moon

• Tidal currents are responsible for 50% of the marine energy delivered to the coast

Littoral cell

A simplified model that examines coastal processes and patterns in a given area

Shoreline management plan (SMP)

A strategy to manage flood/erosion risk along a particular stretch of coastline, usually extending across council boundaries

Wave refraction

Where the coastline is not uniform, waves do not break parallel to each other. Instead wave energy is concentrated onto headlands and dispersed in bays.

Eustatic sea level change

The global change in sea level relating to volume of water in the ocean

Terrestrial change

The variation in height of the land in relation to the sea

Isostatic sea level change

the localised or "isolated" change in land and sea level relative to each other

What kind of coastline is associated with relative fall in sea level?

Emergent

What kind of coastline is associated with relative rise in sea level?

Submergent

What landforms are associated with advancing coastlines/ deposition?

Beaches, spits, bars, tombolos, sand dunes and cuspate forelands

What landforms are associated with retreating coastlines/ erosion?

Steep cliffs, wave-cut platforms, caves, arches, stacks and stumps

Explain the formation of a raised beach

A raised beach is above the current sea level. This is formed by ice melting leading to an uplift of the land (rebound) when the pressure is released (isostatic change)

Explain the formation of a fjord

A fjord is a glacial valley flooded by the sea caused by the rise in sea level that takes place when ice melts (eustatic change)

Mass movements

Any of the processes of erosion, transport and accumulation that can occur on slopes due to gravitational forces

Mechanical weathering

Weathering caused by physical processes such as freeze-thaw

Biological weathering

Weathering caused by living things- eg. plant roots or animal burrows

Chemical weathering

Weathering caused by chemical reactions such as acid rain

Bio-chemical weathering

Weathering caused by products of metabolism- eg. bird feces

Water-layer weathering (hydration)

Weathering due to tidal changes causing wetting and drying

Salt weathering

The breakdown of rock caused by salt, either by its chemical composition or by its growth/expansion

Give features of constructive waves

-Low frequency (6-8/min) -Strong swash, weak backwash -Depositional -Low wave height in proportion to length -Low gradient and energy

Give features of destructive waves

-High frequency (10-12/min) -Weak swash, strong backwash -Erosional -High wave height in proportion to length -High gradient and energy

Why do wave power and wave height vary globally?

Differences in wind strength. The highest waves occur in the Southern Ocean and the North Pacific where they are generated by the strongest winds.

When does wave refraction occur?

When waves approach an irregular coastline or approach the coast at an oblique (slanting) angle

Where does wave refraction concentrate the most energy?

Headlands

What is meant by "sub-aerial processes"?

It is an umbrella term for the processes of weathering and mass movement

What are the three types of rock?

Igneous (formed as a result of tectonic activity) Metamorphic (formed by other rocks being superheated under pressure) Sedimentary (formed by the accumulation of sediment)

What characterises a "drift-aligned" coastline?

Prevailing wind dominates wind direction and waves approach the coast at an angle. There is higher rates of longshore transportation of sediment

What characterises a "swash-aligned" coastline?

When prevailing winds cannot influence wind direction due to an offshore barrier such as an island. Waves approach the coast parallel to the shore and there is less loss of sediment by longshore drift

What is meant by "rock strata"?

The layers of rock

What is meant by "lithology"?

The characteristics of rocks associated with their resistance, bedding, jointing and permeability

What effect is produced by horizontal beds of rock on the coast?

Steep cliffs with notches

What effect is produced by rock beds dipping seaward?

Gentler slopes that are less stable and prone to mass movement

What effect is produced by rock beds dipping inland?

Steeper, more stable cliffs

Traction

Large, heavy pebbles are rolled along the sea floor.

Saltation

Pebbles are bounced along the sea floor.

Suspension

Lighter sediment is suspended (carried) within the water.

Solution/corrasion

The transportation of material dissolved in the water.

ENSO

El Niño Southern Oscillation (refers to both la niña and el niño)

Upwelling

An instance of seawater, magma or another such liquid rising up

What is the importance of ocean currents?

They distribute warmth and moisture around the planet. Heat energy is moved from areas of surplus (near the equator) to deficit (near the poles) making regional temperature differences much less extreme.

Thermocline

The gradient of temperature differences in a body of water such as the ocean

Halocline

The salinity gradient within a body of water such as the ocean

Pycnocline

The gradient of water density within a body of water such as the ocean (associated with changes in temperature)

Gyres

Large systems of circular ocean currents formed by global wind patterns and the coriolis effect. There are five large permanent gyres around the globe.

Ekman Spiral

A displacement of ocean current associated with the Coriolis effect

Thermohaline currents

Deep-ocean currents driven by differences in the water density/temperature (thermo) and salinity (haline)

Surface Currents

Ocean currents up to 50-100 metres deep driven by wind

Deep Ocean Currents

Ocean currents under 100m in depth driven by thermohaline circuation

Which factors can influence ocean currents?

Winds, water density, salinity, temperature, tides, sea floor topography, coriolis effect

What are the three main types of rainfall?

Convectional, relief and frontal

Convectional rainfall

Water is warmed and evaporates leading to the incidence of condensation and precipitation later

Relief rainfall

When water in the air makes contact with land of a specific height it is forced to condense and become rainfall

Frontal rainfall

Moisture from the air becomes rainfall when warm air meets cold air

Mangroves

Salt-tolerant plants that grow in tidal areas

What is ENSO?

El Niño Southern Oscillation- a single climatic phenomenon with three states: neutral, el niño (reversal of normal conditions) and la niña (intensification of normal conditions)

ENSO: neutral conditions

Sea-surface temperatures are close to the average. Convective circulation flows from South America to SE Asia.

Impact of la nina in Eastern Pacific (South America)

Normal conditions are intensified: low pressure, cooler ocean temperatures=higher yield for fishing industry, can cause severe drought in coastal areas, increased risk of respiratory disease due to high humidity

Impact of el nino in Eastern Pacific (South America)

Normal conditions are reversed: warm water= more evaportative precipitation, there can be flooding, decline in aquatic life and increased malaria outbreaks as a result of mosquitoes having more breeding ground over floodwater

Impact of la nina in Western Pacific (Australia, SE Asia)

Intensification of normal conditions: farmers benefit from increased rainfall (eg. lettuce and rice in Vietnam), heavy rain=mudslides, increased flood risk

Impact of el nino in Western Pacific (Australia, SE Asia)

Reversal of normal conditions: High pressure, colder water, drier conditions, famine, droughts/bushfires

Territorial waters

-the zone extends 12 nautical miles offshore

-the country’s laws are sovereign

Exclusive economic zone

-200 nautical miles offshore

-However continental shelf (ie. sea bed) can extend sovereignty over 220 miles

The High Seas

-All areas outside of countries’ EEZs

-Subject to international jurisdiction so one country can prosecute another (eg. USA, Somalian pirates)

What is the freedom of the seas doctrine?

A principle put in place during the 17th century limiting national jurisdiction to a narrow belt surrounding the country. It was rethought in the 20th century due to concerns over pollution and depletion of fish stocks.

What is UNCLOS?

United Nations Convention of the Law of the Sea

What is meant by “soft power?“

The ability of a nation to exert control through economic, political or cultural means

What do the oceans contribute to humans?

-Food: 200 billion pounds fish and shellfish caught each year

-Recreation

-Mineral mining

-Mitigating against climate change

-etc.

The problem of overfishing

-1/3 of global fish stocks are overexploited

-eg. cod stocks in the North sea are less than 10% of their level in 1970

-fisheries will have to close- loss of livelihood

-disruptions of natural ecosystems and food chains

Potential solutions to overfishing

-Marine protected areas (limiting fishing)

-The EU common fisheries policy (1983) provided funding to finance a reduction in fleet sizes

-Aquaculture (ie. fish farming)

What conditions do hurricanes require to form?

-A source of warm, moist air derived from tropical oceans with a sea surface temperature of over 27 degrees C

-Sufficient distance from the equator to provide spin (between 5 and 30 degrees N or S)

-Low wind shear

-Winds converging from different directions causing air to rise and storm clouds to form

Arguments for ocean floor mining

-We need minerals such as cobalt for component in electric things for the “green revolution“

-Traditional cobalt mining is associated with child labour

-Demand for components is forecast to grow faster than traditional mining methods can supply

Arguments against ocean floor mining

-Affects areas rich in natural biodiversity

-Disrupts deep oceans which are important in regulating climate, absorbing heat and cycling nutrients

-Loss of species and biodiversity

Where is nitrogen stored in the oceans?

In water, in organisms, in decomposing matter, in the ocean floor and in fossil fuels

Where is carbon stored in the oceans?

Dissolved CO2 (carbonic acid) in organisms, dead and fecal matter, fossil fuels

What are some impacts of ocean acidification?

• Makes growth difficult for corals and other organisms with shells or exoskeletons

• Corals rarely grow back

• Some fish struggle to detect predators

• Can wipe out food chains