Option Theme - Oceans and their Coastal Margins Flashcards
Why is the gulf stream important in the UK ?
- brings warm water to west coast of Europe from Gulf of Mexico across the Atlantic Ocean
- heats land + so keeps weather reasonably mild
- regulation of our climate is especially good for primary industries e.g. agriculture as it brings predictability
- without the gulf stream, we would experience Arctic-like conditions
Abyssal plain
- The abyssal plain is at the edge of continental slope
Seamounts
Extinct volcanic cones that lie below the surface
Guyot
A guyot is a flat-topped volcano that reached the surface but later subsided
Mid-ocean ridges
- Linear belt of submarine mountains
- Occur at constructive plate boundaries
- New magma forces its way between 2 plates and pushes them apart
Ocean trenches
- deepest parts of the ocean
- formed at subduction zones
Oceanic water // how do temperature, salinity and pressure affect density ?
- high temps. = less dense water
- high salinity + pressure = more dense water
Oceans and climate // what is specific heat capacity and how does this affect sea and land temperatures ?
- specific heat capacity = amount of energy it takes to raise the temperature of a body
- it takes more energy to heat up water than land
- it takes longer for water to lose heat
- places close to the sea are cool by day, but mild by night
Oceans and climate // surface ocean currents (gyres)
- caused by prevailing winds blowing across ocean
- dominant flow of surface ocean currents is circular
Oceans and climate // what is the great ocean conveyor belt ?
A global thermohaline circulation, driven by the formation + sinking of deep water + responsible for the large flow of upper ocean water
It begins in polar regions where cold salty water sinks into the depths + makes its way towards the equator
El Niño // what is it ?
A warming of the eastern Pacific that occurs at intervals between 2 and 10 years, and lasts for up to 2 years
El Niño // Normal conditions in Pacific Ocean
- Walker circulation = east-west circulation that occurs in lower latitudes
- Near South America, winds blow offshore, causing upwelling of cold, rich waters
- Warm surface water is pushed into western Pacific
- Normally, sea surface temperatures (SSTs) in western Pacific are 28degrees+ causing low pressure + high rain
- over coastal SA, SSTs are low = high pressure + dry
El Niño // el niño conditions in pacific ocean
- during el niño episodes, pattern is reversed
- warm water from west Pacific flows into east Pacific
La Niña
- intermittent cold current that flows east across equatorial Pacific Ocean
- an intensification of normal conditions
- has been linked w. unusual rainfall patterns in Sahel + India
El Niño + La Niña // how can we manage the impacts
- sensors across Pacific predict El Niño months in advance
- last one predicted so far in advance that Peru was supplied with food + people moved from vulnerable areas
El Niño + La Niña // why is it difficult to manage the impacts
- affect large parts of globe, not just Pacific
- some countries do not have resources to cope
- indirect impacts across world on trade and aid
Effects of 1997-8 El Niño
- Phillipenes // drought reduced rice harvest by 15%
- China // drought affect 20million ha arable land in north
- China // grain harvest threatened by flooding in south
- Colombia // fish catches down 20%
Oceans and resources // continental shelf
- oil and gas deposits
Oceans and resources // ocean floor
gold and manganese
Oceans and resources // fish
- worldwide fish harvest in 1900 was 5million tonnes
- in 2000, 90million tonnes
- 10% of protein eaten by people
Oceans and resources // underwater cables
- continental shelf + open ocean have been used for laying of cables
- an internet blackout in Jan.2008 left 75million people without access was caused by 1 ship that tried to moor off Egypt coast in bad weather
- highlighted fragility of global communications network
- economies across Asia + Middle East struggled to cope
Why have total fish catches remained high, despite overfishing ?
- larger, predators fish eat large quantities of small fish
- as their numbers fall, numbers of small fish rise
- this may change marine ecosystems for ever
- despite overfishing of cod etc. total catches remain high
- but type of fish caught changing
Impacts of overfishing
- 70% of world stocks in need of management
- Canada, Newfoundland: Grand Banks collapsed in 1992
- Black Sea: pollution meant extinction of 14 fish species
The closure of Grand Banks
- Grand Banks off Newfoundland once world’s richest fishery
- in 1992 closed to allow stocks to recover
- expected to be closed for 3 years
- fish numbers, esp. cod, still not recovered so still closed
- cod’s niche in ecosystem taken by other species e.g shrimp + langoustines
How can small meshed nets encourage conservation of resources?
Small meshed nets protect juvenile fish and encourage breeding
How can quotas encourage conservation of resources?
- match supply to demand
- plan quota uptake throughout the season
- protect sensitive stocks
Other methods of encouraging sustainable fishing
- apply penalties for overfishing and illegal landings
- limit number of vessels
- finance investment in fleet modernisation
- large license fees to discourage small, inefficient boats
How much of the carbon dioxide emitted into the air by human activity is absorbed by the sea
Oceans moderate climate change by absorbing 1/3 of carbon dioxide emitted into the air by human activity
How much marine pollution comes from land-based activities ?
Over 80% of marine pollution comes from land-based activities.
When were single-hulled ships banned and what should be the impact of this ?
Oil spills should have become rarer after 2010, when all single-hulled ships were banned
Radioactive effluent also makes its way into the oceans. How was the Arctic Ocean used by the Soviet Union between 1958 and 1992 ?
Between 1958 and 1992, the Arctic Ocean was used by the Soviet Union as the resting place for 18 unwanted nuclear reactors, several still containing their nuclear fuel
Response to ocean threats // 1972 Stockholm Convention
- governments urged to control dumping of waste in oceans by implementing new laws
- International Maritime Organisation given responsibility for this convention + protocol adopted in 1996
What is an Economic Exclusive Zone (EEZ) ?
An economic exclusive zone (EEZ) is an area in which a coastal nation has sovereign rights over all the economic resources of the sea, seabed and subsoil, extending up to 200 nautical miles from the coast
Why are countries around the Arctic Ocean rushing to stake claims on the Polar Basin seabed and its oil and gas reserves ?
- improve oil drilling access
- open up the Northwest Passage, a route through the Arctic Ocean linking the Atlantic and Pacific
Give some examples of countries staking their claim on the Arctic
- Canada is establishing a year-round Arctic presence on land + sea + air
- Denmark is trying to prove a detached part of the underwater Lomonosov ridge is an extension of Greenland, which is Danish territory
How much of the world’s oil and gas reserves could the Arctic hold ?
- the Arctic could hold 1/4 of world’s undiscovered gas + oil reserves
- this amounts to 90 billion barrels of oil
Why have environmental groups criticised the scramble for the Arctic?
- it will damage unique animal habitats
- they have called for a treaty similar to that regulating the Antarctic, which bans military activity + mineral mining
What does the 1982 UN Law of the Sea Convention state and why has this created a tangle of overlapping Arctic claims ?
Under the 1982 UN Law of the Sea Convention, costal states own the seabed beyond existing 370km zones if it is part of a continental shelf of shallower waters
What percentage of the world’s fishing regions fall under a country’s EEZ ?
Up to 98% of the world’s fishing regions fall under an EEZ
Name a geopolitical ocean conflict
Croatia’s ZERP (ecological and fisheries protection zone) // in the Adriatic Sea, caused friction with Italy and Slovenia and caused problems during Croatia’s accession to the EU
Croatia’s ZERP // what happened and why
- 1 Jan 2008, zone came into full effect stopping fishing from other countries
- Prior to ZERP’s declaration, Italian ships caught €300 million worth of fish from zone p/a - 10x more than croatia
- In 2008, 1/3 all Italian fishing activity came from zone
- EU urged (would be member) Croatia not to enforce controversial fishing zone due to disagreement from Italy + Slovenia
- In March 2008, Croatia decided not to enforce ZERP for EU members
- Any fishing boats (non-EU) caught inside area are escorted outside by navy + fisherman arrested
Features of coastal margins // geology properties // differences between hard and soft rocks
- hard rocks e.g. granite + basalt give rugged landscapes e.g. Giant’s Causeway, Northern Ireland
- soft rocks e.g. sand + gravel give low, flat landscapes
e. g Poole Harbour, south coast England
Features of coastal margins // geological structure // concordant + discordant
- concordant = parallel to coastline e.g. south coast of California
- discordant = geological strata perpendicular to coastline e.g. south west coast of Ireland
Features of coastal margins // processes // erosional landscapes vs. areas of rapid deposition
- erosional landscapes contain many rapidly retreating cliffs e.g. east coast of England
- areas of rapid deposition contain sand dunes + coastal flats e.g. the Netherlands
Speed and height of tsunamis ?
- can reach heights of 15m
- can travel at speeds of up to 600km per hour
What is wave energy controlled by ?
- wind strength + duration
- fetch, or distance of open water
- depth of the seabed
What are the main features of constructive waves ?
- they are depositional waves
- capable of travelling very long distances
- long wavelength, low height
- swash greater than backwash
- low energy
What are the main features of destructive waves ?
- generated by local winds + travel only short distance
- they are erosional waves
- short wavelength, high height
- backwash greater than swash
- high energy
What is wave refraction and what does it do ?
- wave refraction occurs when waves approach an irregular coastline
- refraction reduces wave velocity + (if complete) and causes wave fronts to break parallel to each other
- wave refraction concentrates energy on flanks of headlands + dissipates energy in bays
Wave refraction is rarely complete. What happens as a consequence ?
Refraction is rarely complete + consequently longshore drift occurs
How does longshore drift transfer sediment along a beach ?
- swash carries material up the beach in a direction parallel to the prevailing wind
- backwash operates perpendicular to the shore owing to the steepness of the beach slope
- result = net transfer of sediment along a beach
Coastal erosion // sub-aerial erosion
- surface runoff
- rain wash
- weathering by wind + frost
- mass movement // soil creep, landslides, slumps
Coastal erosion // corrosion
- salt crystallisation disintegrates weaker layers
- blue-green algae help break down rock
Coastal erosion // biotic factors
burrowing and browsing organisms
Coastal erosion // abrasion
wearing away of cliff by material (rocks, sand) hurled against it
Coastal erosion // human activity
- can increase runoff + erosion through buildings etc…
- build sea defences
Coastal erosion // solution
dissolving of limestone + other minerals by carbonic acid in seawater
Coastal erosion // attrition
wearing down of broken materials into smaller, more rounded particles
Coastal erosion // hydraulic pressure
compression of trapped air + sudden release
Coastal erosion // salt weathering
The process by which sodium + magnesium compounds expand in cracks, thereby weakening rock structures
Coastal erosion // freeze-thaw weathering
The process whereby water freezes, expands + degrades jointed rocks
Coastal erosion // water-layer weathering
Refers to the tidal cycle of wetting and drying
Coastal erosion // biological weathering
Is carried out by molluscs, sponges + urchins and is important in low-energy coasts
How are sea caves, arches, stacks and stumps formed?
- rapid erosion occurs on weaker points in rocks
- faults in rock may be eroded to form sea caves
- if 2 caves meet, an arch is formed
- if the arch roof collapses, a stack is formed
- if stack is eroded, a stump is formed
How are wave-cut platforms formed?
destructive waves hit against the cliff face, causing undercutting between the high and low water marks, creating a wave-cut notch.
What is a tombolo and how is it formed ?
- a bar that links an island to the mainland
- e.g. Llandudno, Wales
- wave refraction around the island results in a wave energy shadow where increased deposition occurs
What is a bar and how is it formed ?
- a ridge that blocks off a bay or river mouth
- common in areas with low tidal ranges, dominated by swell waves
- e.g. Loe Bar in Cornwall
What is a spit and how is it formed ?
- a beach of sand / shingle linked at one end to land
- found on indented coasts or at river mouths
- e.g. Spurn Head, England
What are sand dunes and how are they formed?
- sand dunes are widespread depositional landforms
- develop with strong offshore winds + large expanses of sand that dry out at low tide
Risks to sand dunes
HUMANS: we mostly have the right to roam across dune systems // this causes erosion as footfall displaces sand
PLANT DAMAGE: farmers allow their animals to graze on the vegetation
Studland Bay: sand dune system
- area of sand dunes in a nature reserve
- these are dynamic but often unstable + vulnerable environments
- due to high tourism, vulnerable areas + recently planted marram grass (to stabilise dunes), the dunes are fenced off to limit access and damage
How is it possible to manage dune systems ?
- dunes play an important role in protecting low lying regions of land e.g. Cambersands
- stagger grazing patters to control vegetation removal + growth
- educate visitors about erosion // info. boards
- encourage growth of more plants e.g. marram grass
- stabilise dunes using old christmas trees
- build a boardwalk
Coastal conflicts: tourism in St Lucia // overexploitation of the sand
- significant increases in beach erosion + environmental degradation
- threatened nesting grounds of endangered turtles
- whilst many hotels artificially replenish beaches, the introduced sand is rapidly eroded
- this causes problems for offshore coral reefs, that require clear water
Coastal conflicts: tourism in St Lucia // over-abstraction of water
- lead to a decline in amount + quality of water available
- as freshwater supplies decrease, saline water intrudes into aquifers so contaminates supply
- tourists are huge consumers of energy + water, reducing supply for local people
Coastal conflicts: tourism in St Lucia // marine pollution
- arising from discharge of poorly treated wastewater into coastal waters
- nutrient loading has led to loss of coral productivity
- discharge of sewage by yachts also contributes to nearshore marine pollution
Holderness - coastal conflict // stakeholders
- farmers
- residents
- local council
- gas workers
Holderness - coastal conflict // background
- Holderness coast in north east England
- one of most vulnerable coastlines in world
- retreats at rate 1-2m every year, mainly during storms or tidal surges
Holderness - coastal conflict // problems caused by
- strong prevailing winds create longshore drift that moves material south along coastline
- cliffs are made of a soft boulder clay // it will therefore erode quickly esp. when saturated
Holderness - coastal conflict // how do the cliffs erode ?
- soft boulder clay cliffs become saturated with rainwater + lose their strength
- cliff is too steep and falls, either as a block of material or as a slurry slide
- cliff failure reduces angle and prevents further erosion
- larges waves from North East remove debris in longshore drift to the south + the cliff oversteepens, rain falls and the cycle begins again
Holderness - coastal conflict // coastal defences // Groynes at Mappleton
Groynes at Mappleton stop the flow of sand down the coast. This has been effective at Mappleton, but there is less sand available for the rest of the coastline, meaning more erosion to the south
Holderness - coastal conflict // coastal defences // Riprap at Withernsea
Riprap at Withernsea stops erosion by dissipating the waves energy. Very effective at Withernsea and has lead to increase in tourism due to a larger beach
Holderness - coastal conflict // coastal defences // Groynes + gabions at Spurn Point
Groynes + gabions at Spurn Point stop the sand moving down the coastline, slowing down longshore drift. Spurn Point is growing slowly
Holderness - coastal conflict // future
- climate change means rising sea levels
- combined with weak clay + increased rate of erosion, coastline will retreat further
- many houses, businesses + agricultural land will be lost, meaning there will be more coastal conflict in future
Examples of hard engineering at coastlines
- sea walls
- gabions
- groynes
Aim of sea walls
large-scale concrete curved walls designed to reflect wave energy
Strengths of sea walls
- easily made
- good in areas of high density
Weaknesses of sea walls
- expensive
- foundations may be undermined
Aim of gabions
rocks held in wire cages absorb wave energy
Strengths of gabions
cheap (compared to sea walls)
Weaknesses of gabions
- cause erosion on downdrift side
- interrupt sediment flow
Aim of groynes
to provent longshore drift
Strengths of groynes
- relatively low costs
- easily repaired
Weaknesses of groynes
- unattractive
- small scale
- may be removed in heat storms
Examples of soft engineering at coastlines
- offshore reefs
- beach nourishment
Aim of offshore reefs
waste material e.g. old tyres weighted down, to reduce speed of incoming wave
Strengths of offshore reefs
- low technology
- relatively cost-effective
Weaknesses of offshore reefs
long term impacts unknown
Aim of beach nourishment
sand pumped from seabed to replace eroded sand
Strength of beach nourishment
looks natural
Weaknesses of beach nourishment
- expensive
- short-term solution
Why was fish farming first introduced ?
Fish farming was first introduced when overfishing of wild Atlantic salmon caused their populations to crash
What is a coral reef ?
A ridge in a relatively shallow, tropical sea, consisting of colonies of coral + other organic matter
How do mangroves help to maintain the health of coral reefs ?
- mangroves protect coral reefs from sedimentation from land-based sources
- help to keep water clear of particles + nutrients
- provide spawning + nursery areas for many animal species that spend their animal lives on the reefs
How do coral reefs help to maintain the health of mangroves ?
- coral reefs provide shelter from the impact of waves + storms for the mangroves + their inhabitants
- the calcium carbonate eroded from the reef provides nutritious sediment from which the mangroves grow
How biodiverse are coral reefs?
- coral reefs contain nearly 1 million species of flora + fauna
- 25% of the world’s sea fish breed, grown, spawn and evade predators in coral reefs
How at risk are coral reefs from human activity?
- 25% coral reefs have already disappeared
- 2/3 of world’s coral reefs are at risk from human activity
- 58% of the world’s coral reeds are at high / medium risk of degradation
- 80%+ of South East Asia’s extensive reef systems are under threat
When does coral bleaching occur ?
When corals are stressed by changes in conditions such as temperature, light or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white
What are the growth requirements of coral reefs?
- warm water: constant temp (between 17-34 degrees)
- salinity: 30-38 parts per thousand
- sunlight: for photosynthesis (esp. plant based corals)
How do pollution, sedimentation + global climate change threaten coral reefs?
They impede light penetration in the water, effectively halting the photosynthesis of the living part of the coral reefs
How does deforestation reduce the amount of sunlight that a coral reef system revives?
Increased soil erosion + surface runoff (due to overexposure to weather due to deforestation) causes blooms of sedimentation in the sea, acting as a barrier between the sun and the coral
Value of coral reefs to humans
ECONOMICS: generate $375billion in annual revenue
EROSION CONTROL: protects coastlines of 109 countries (intercepts wave energy)
BIODIVERSITY: home to 25% of fish species
MEDICINE: untapped pharmaceutical resource
FOOD: basis for 10% of world’s diet
What are the main threats to coral reefs?
- dynamite + cyanide fishing
- sedimentation
- cyclones + tropical storms
- tsunamis (many areas of coral in Indian Ocean destroyed by 2004 tsunami)
Coral case study: The Southern Islands, Singapore // background
Singapore’s coral reefs home to nearly 200 species of hard corals, with a large tourist industry and both commercial + sport fishing
Coral case study: The Southern Islands, Singapore // threats
Land reclamation programmes + the regular dredging of shipping channels have resulted in widespread sedimentation of the reefs
Coral case study: The Southern Islands, Singapore // why have they been able to survive?
Strict controls on sewage + pollution have meant that the reefs have been able to survive, despite their proximity to such a densely populated country
Coral case study: The Bolinao Reef, the Philippines // threats
- main threat to the reefs are the 20,000 commercial people (not locals) who work in fishing
- increasing number of Filipinos have migrated here due to loss of farmland
- they now harvest fish + other reef resources
- Bolinao fishers have had their catches reduced to 1kg a day
Coral case study: The Bolinao Reef, the Philippines // solutions
- since 1986, programmes have been introduced such as small scale mariculture of seaweed + invertebrates
- public education + law enforcement have led to a reduction in destructive fishing
- coral cover + fish numbers are increasing
- despite this reef remains in critical state
Coral case study: Kepulavan Seritu, Indonesia
- in 1995, islands were declared a marine national park
- local people have since relied on increased tourism this status has brought
- domestic sewage + industrial waste from Jakarta threaten the area
- dynamite fishing (although outlawed nationally in 1920) still occurs
- no strategy to promote sustainable tourism
- global recession has seen visitor numbers decrease
What are mangroves ?
Mangroves are salt-tolerant forests of trees + shrubs that grow in the tidal estuaries and coastal zones of tropical areas.
What percentage of tropical coastlines do mangroves cover ?
Mangroves once covered 75% of the world’s tropical coastlines. Now they only cover 25%.
How do mangroves survive ?
- filter 90% of the salt found in seawater as it enters their roots
- mangroves store freshwater in thick succulent leaves // a waxy coating on leaves seals in water + minimises evaporation
- some mangroves grow roots that stick out of the ground like snorkels // these breathing tubes allow mangroves to cope with daily flooding by the tides
Importance of mangroves to the environment
- stabilise the coastline, reducing erosion from storm surges, currents, waves + tides
- intricate root system allows fish to seek food + shelter from predators
- provide a nursery ground for fish
Economic value of mangroves
- ecotourism
- 1 hectare of mangrove in the Philippines can yield 400kg fish + 75kg shrimp
- trunks + branches diminish erosive power of waves
- natural filter, absorbing nutrients from farming
Why are mangroves being damaged?
- sacrificed for salt pans, aquaculture, housing developments + hotels
- may die from oil spills, chemical pollution and disruption of their sensitive water + salinity balance
How did the Indian Ocean Tsunami (2004) help people understand the importance of mangroves ?
- where mangroves were intact, they served as natural breakwaters, dissipating the energy of the waves, mitigating property damage + perhaps saving lives
- post-tsunami, the logic of allowing a country’s mangrove ‘bioshields’ to be destroyed seemed totally flawed
Why does Bangladesh view mangrove conservation with such importance ?
- a low-lying country with long vulnerable coastline
- 70-80% population live less than 1m above sea level
- high pop. density (more than 1000people / km2)
- by planting mangroves on delta sediments, it has gained 300,000 acres of new land on Bay of Bengal
- today is largest surviving single tract of mangroves in the world
