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Marine processes

Chapter 6

Th e coastline is where the land and the marine environment (seas and oceans) meet. It is like a battle zone, where waves erode, transport and deposit material via a complex set of processes. Th e size and energy of the waves, the strength and direction of the wind, and the type of rocks along the coast create a range of coastal landforms. Features of coastal erosion such as cliff s, wave-cut platforms, caves, arches, stacks, headlands and bays are formed by powerful, destructive waves. Where wave action is more gentle and constructive, features of coastal deposition, including beaches, spits and bars, sand dunes and marsh, are formed.

Coastlines are constantly changing as a result of the action of the sea and through the impact of human activity. Eff orts to protect the coast from erosion and fl ooding can be very costly, but not always eff ective or sustainable. Along some coastal areas, coastal defences are no longer maintained, allowing the sea to reclaim areas of land.

Ports and harbours for industry and shipping are found along coastlines. Coasts also attract millions of tourists every year to beaches, the sea and unique features such as coral reefs. Industry, including tourism, brings valuable income and work to coastal towns, benefi ting the local area and the country’s economy. However, it can also lead to pollution from factories, sewage outlet pipes and oil spills. Th e large numbers of people who visit popular coastal areas may erode footpaths, drop litter, cause traffi c congestion and may lead to competition for space for accommodation and other facilities.

Figure 6.2Diver on coral reef

Figure 6.1Wave action. Caption tbc

M06_GEOG_SB_IGCSE_1197_U06.indd 118 29/4/10 16:41:50

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6.1 Wave actionTh e action of waves shapes the coastline. Some erode the land, others help build it up by transporting and depositing material. Waves vary in size, height and frequency, depending on the strength of the wind and the amount of water they travel over (the fetch). Destructive waves (Figure 6.3a), are high-energy waves, responsible for eroding the coast, resulting in many spectacular landforms. Constructive waves (Figure 6.3b) are low-energy waves, depositing material along and up the coastline.

Figure 6.3(a) Destructive waves; (b) constructive waves

Figure 6.4Longshore drift

Th e action of a wave can be divided into two parts – the swash and backwash. Th e swash is the top part of the wave that breaks and topples over, pushing up the beach. Th e backwash is the water that falls or washes back down the beach. Destructive waves have a stronger backwash and remove material. Constructive waves have a stronger swash and deposit and build up material.

When constructive waves approach the coast at an angle, the swash also moves up the beach an angle, pushing the material they carry up the beach (Figure 6.4). Th e backwash, under the force of gravity, will then fl ow back down the beach at right angles to the sea, taking sand and pebbles with it. Th is is repeated in a zigzag pattern, gradually moving material along the coast by a process called longshore drift . If the coastline changes direction, material will continue to be deposited in the original direction, forming a spit.

Constructive wavesDestructive waves

a b

longshore drift

swash

backwash

direction of incoming waves


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6.2 Coastal erosion Figure 6.5Processes of marine erosion

Figure 6.6Corrasion and hydraulic action

Figure 6.7Beach pebbles rounded by attrition

Figure 6.8Headlands and bays

There are four main processes by which waves erode the coastline (Figure 6.5). High-energy waves crash against the land, hurling sand, shingle, pebbles and rock fragments against it. The force of this breaks up the rock – a process called abrasion. Waves pounding against the rocks along the coast trap air in the cracks within it. As the waves retreat, the air pressure is released. This is repeated, causing large pieces of rock to break away, a process called hydraulic action.

The eroded pebbles and rock fragments carried by waves constantly hit against each other, eroding them into smaller pieces of sand and gravel or into rounded pebbles through a process called attrition. Some types of rock found along the coast contain minerals that can be dissolved by the action of sea water, for example chalk and limestone – a process called solution.

Headland and bays

Rocks vary in hardness. Where hard rocks occur along a coastline, cliffs and headlands are often found. This is because harder rocks erode more slowly. Softer rocks are more easily eroded and wear back more quickly, forming bays. Beaches often form between, and are sheltered by, headlands on one or both sides (Figure 6.8).

Softer rocka)

b)

WA

VE

S

Bay

Bay

Bay

Headland

Erodesmorequicklyforminga bay

Softer rock

Harder rock

Resistant (harder) rock

Erodes slowly leaving a headland

Less resistant(softer) rock

Abrasion

Attrition

Solution

Hydraulic action


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Marine processes

Cliffs

When hard, resistant rocks are found next to the sea, cliffs are formed on headlands. Figure 6.9 shows how they are formed by destructive waves eroding the headland. This creates a notch at the base of the headland at sea level. As erosion continues, unsupported rock first overhangs, then collapses. The backwash of the waves here is usually stronger than the swash, so smaller pieces of rock are quickly removed from the base of the cliff. Over time the cliff will be eroded and will retreat inland, leaving behind a rocky platform called a wave-cut platform, covered at high tide, but visible at low tide (Figure 6.10).

Cliff structure

Figure 6.9Cliff formation and retreat

Figure 6.11The effect of rock structure on cliff shape

Figure 6.10Cliff and wave-cut platform

cliff retreats

original position of cliffwave cut notch

low water mark

wave cut platform

high watermark

gently sloping cliff facewith few overhangs

steep cliffface withmanyoverhangs

rugged cliff top

cliff top slopessteeply down inland

waveerosion

The structure, as well as the hardness, of rocks will affect the shape of cliffs (Figure 6.11). Horizontal layers or bedding will form steep cliffs (Figure 6.11c). Where the layers dip inland, away from the sea, the cliff face will be steep and uneven (Figure 6.11a). If the layers dip towards the sea, the cliff face will have a more gentle slope (Figure 6.11b). Sometimes cliffs are formed from rocks of differing hardness. This will create an uneven surface as they are eroded or weathered at different rates.

a b c


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Headland erosion

When waves approach headlands they are bent or refracted. As a result they attack the headland on three sides. Weaknesses in the rock will be eroded first – a small crack or joint will be enlarged to form a sea cave. If waves break through to the other side of a headland they form an arch. The roof of the arch may later collapse, leaving a stack – a tall outcrop of rock standing on its own away from the headland. Stacks are eventually worn away to leave stumps, sometimes visible at low tide.

Figure 6.13Headland with arch/stack tbc

Figure 6.12Headland erosion and retreat

softer rock

softer rockharder rock

stack

stumparch

waves attackweaknessesin rock cutting sea cavesand arches


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6.3 Coastal deposition

Beaches

Beaches are formed when material eroded from the land is transported by the sea and deposited along the coastline. This material is known as the beach store. It occupies the zone between the low and high water marks. Figure 6.14 shows how longshore drift affects the beach store. The main sources of beach material in Figure 6.14 come from:

A erosion of the cliff provides rock fragments

B longshore drift carries sand and pebbles from the cliff to the beach

C constructive waves push the sand and pebbles up the beach making it higher and wider

Where rivers flow into the sea, fine muds and gravels may be picked up by waves and added to the beach store.

Figure 6.15 shows the shape of a typical beach. Few beaches have a smooth profile – most rise from the sea in a series of ridges, called berms. These ridges are built by constructive waves pushing material up the beach. If there is a very high tide, a berm will form high up the beach. Material deposited here becomes stranded and tends to remain in place, with only small amounts washed back by the backwash. Berms further inland are usually higher and composed of larger pebbles. During low tides berms are formed closer to the sea.

Figure 6.14Building beaches

Figure 6.15Beach structure showing berm

Figure 6.16Grading of beach material by size – smallest nearer the sea

cliffs

beach

land

berms

longshore drift carriesbeach store along coast

A

B

C

constructive waves throw sand and pebbles up the beach

sea

berms are found at different tide levels

BEACH STORE


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Spits and bars

If longshore drift is taking place, sediment is gradually moved along the coast. Sometimes the coastline changes direction, or there is a river mouth or bay. Sediment (sand and shingle) will continue to be deposited by longshore drift, building up and out from the coast and roughly parallel to it. This feature is called a spit (Figure 6.17). Behind the spit is a sheltered area where a saltmarsh may often be found. If the spit continues to grow, it can cut off the river’s route to the sea completely, forming a bar (Figure 6.17). Occasionally a spit may grow and join onto an offshore island forming a feature called a tombolo. The water trapped between the coast and these features is called a lagoon. Figure 6.18 shows Spurn Head, a spit on the Humber estuary in the UK. Wave action has caused the spit to bend and curve. You can see sediment and saltmarsh located on the inside curve of the spit.

Figure 6.17The formation of spits and bars

Figure 6.18Spurn Head, UK

NOriginal coastline

Headland

Longshoredrift

Prevailing windsSea

Spit

River estuary

Bar

The spit blocksthe estuary toform a bar

Deposition at the end of beach (longshore drift)


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Saltmarsh

Figure 6.20Sand dunes along the Lincolnshire coast, UK

Figure 6.21Marram grass

Figure 6.19Saltmarsh, Lincolnshire coast, UK

If a coastal area is flat and muddy, saltmarsh may form in sheltered locations, e.g. behind spits, sea defences, creeks or inlets, where sediment can be deposited and can accumulate. Saltmarsh is usually fully or partly covered at high tides and revealed at low tide – so they are inter-tidal zones. They have a highly specialised range of plants that have to be able to tolerate not only salt water but also drier conditions when the tide retreats. They are highly biodiverse habitats that can absorb wave energy and protect the coast from erosion and flooding.

Coastal sand dunes need a large supply of sand to form, so they are found inland behind large sandy beaches. If the beach is exposed, winds from the sea pick up sand, which starts to accumulate around obstacles such as vegetation or large rocks and pebbles. This then accumulates into small ridges and dunes begin to form. The process continues, and older dunes move inland as new ones form next to the beach.

Some sand dune coasts are continually changing, whilst others may have been formed hundreds of years ago and remain unchanged along the coast. Erosion by the wind, storm waves and human activity is a constant threat. Typically marram grass (Figure 6.21), with its long roots, is planted to stabilize sand dunes, although other measures such as fencing and sand traps are also used. On established dunes a clear pattern or succession of vegetation colonisation occurs. The older the dunes, the more variety.


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6.4 Managing coastal areasMarine environments, especially coastal areas, face a number of conflicting pressures. Although the coast may be considered a natural environment, in reality much of it is far from natural and is highly managed (Figure 6.22) or strongly affected by human activity. With a number of different users, there is usually a range of opinions about which part should be protected – and how.

Over the next four pages we will look at some of the ways in which we manage the coast, especially in terms of sea defences and the impact of industrial development. Other case studies in the book also deal with management and pressures on the coast. These include mass tourism in the Mediterranean (p.X, section 10.4), The Great Barrier Reef (p.x, section 6.7) and marine pollution (p.X, section 6.8). The effect of the impact of natural hazards on marine environments is also dealt with – the Asian tsunami (p.x, section 3.5) and Hurricane Katrina (p.x, section 7.6).

Coastal protection

We need to protect areas of coast where erosion is at its greatest, or buildings, roads and valuable land could fall into the sea. One of the most visible signs of coastal management are the different methods we use to defend the land. These are divided into two types – hard engineering and soft engineering methods. Figure 6.23a and b shows the main types, and their advantages and disadvantages.

Figure 6.23aHard engineering methods

Figure 6.22A stretch of managed coastline

Type Description Advantages Disadvantages

Sea wall Vertical, hard, (usually) concrete walls. Sometimes curved to reflect wave energy back out to sea

Prevents erosion; protects land and buildings etc; can include amenities, e.g. promenade; may stop land flooding

Expensive to build and maintain; unsightly; wave power not dissipated; can increase erosion of beach

Groynes Wooden barriers built along the beach at right angles

Quick to construct; protects beach – beaches absorb wave energy; prevents longshore drift

Can starve beaches of material downdrift; needs continual maintenance; gives uneven beach

Rip rap/boulders/rock armour/revetments Large boulders piled up at the top of the beach, called gabions if secured inside wire cages. Revetments may sometimes be constructed of concrete/wood

Relatively cheap; low maintenance; dissipates wave energy; helps beaches retain material; flexible use

Can be unsafe; may need a lot of space/cover large area to be effective


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Type Description Advantages DisadvantagesBeach nourishment/beach replenishment Replaces eroded

beach material – usually dumped by lorries and then spread evenly over beach area

Beaches absorb wave energy, less reaches land = natural defence; fairly cheap

Needs constant maintenance; replacement sand source required

Sand dunes Ridges of sand behind beaches, created by onshore winds

Natural defence; attractive; dissipate wave energy; provide habitats for plants and wildlife

Constant maintenance; very easily eroded by wind, water or storms

Managed retreat Allowing an area of coast to become eroded without protecting it

Cheap; Allows, e.g., saltmarsh, beaches and provide natural coastal protection

Not appropriate if land is of high value; difficult to control once started – may have unexpected results

Most coastal areas inhabited by people are defended by a combination of these methods. For example, along the Pembrokeshire coast in Saundersfoot Bay, a range of measures are in place (Figure 6.24). There are also places, such as Amroth, where zero action is considered – either allowing the sea to erode by having no defences, or not maintaining existing defences and allowing the sea to reclaim the coast.

Figure 6.23bSoft engineering methods

Figure 6.24Sea defences, Saundersfoot Bay, Pembrokeshire

NTelpyn Point

East Amroth

Amroth

Wiseman’sBridge

Saundersfoot

MonkstonePoint

Saundersfoot Bay

0 1kilometres

2

Curved sea wallWooden groynesConsidering

zero action

GabionsRiprap

Vertical sea wallWodden groynesBeach replenishment


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6.5 Managing coastal areas Case study: Milford Haven, Pembrokeshire, South Wales (MEDC)

Figure 6.26Tanker docking in Milford Haven tbc

Figure 6.25Milford Haven land use

oil refineriesand terminal

Key

power stationPembrokeshireCoastal PathPembrokeshire CoastNational Parkrock platform

cliffs beachdeposits

jettyjetty

Milford Haven

jettiesjetty jetty

Stack Rock

Thorn Island

locationofMilfordHaven

3 km0

N

Milford

Haven

Milford Haven is a natural deep-water inlet formed when sea levels rose at the end of the last ice age, drowning a wide river valley to form a feature called a ria. The whole coast around the Haven is deep water, on the edge of the Atlantic Ocean, and the land rises steeply inland. A wide range of human activity is found here, from tourists visiting the stunning scenery of the Pembrokeshire Coastal Path and National Park, to supertankers bringing crude oil to the refineries around Milford Haven port (Figure 6.25)

Milford Haven Port Authority factfile

were bigger ships carrying more cargo

Industry

Its location on the UK’s Atlantic coast, its deep water and sheltered nature make Milford Haven an ideal location for a port. The port has facilities for both oil and liquid natural gas (LNG) tankers, with a number of refineries


Image to be updated

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Marine processes

situated around it. Tankers dock and offl oad at a series of specialised jetties that reach out to the deepest water. Pipelines distribute oil and gas inland to other facilities. Other industries and facilities include a power station, with a new LNG-powered one planned for the future; a 360-berth marina; facilities for the fi shing fl eet; shopping, transport and fi nancial services.

Industry versus environment

Th e port of Milford Haven is surrounded by some of the best coastal scenery in the UK (Figure 6.27), the Pembrokeshire Coast National Park. It has a mixture of steep, rocky cliff s and sandy beaches, forested estuaries and hills, castles and forts, covering 620 km2. Th e coastal path itself is 416 km in length. Th ere is a wide range of sites of special scientifi c interest (SSSIs), diff erent habitats, nature and marine reserves and other conservation areas. Th e National Park Authority is responsible for conserving the area and planning its development and use.

Mixing industry with an attractive, protected environment can present problems. In February 1996, the oil tanker Sea Empress was blown onto the Milford Channel Rock and ran aground as it approached Milford Haven (Figure 6.28). Rescue tugs tried to free the tanker in the days immediately aft er the accident, but were unable to do so. Th e weather worsened and gale force winds hit the ship. A total of 72 000 tonnes of crude oil and 500 tonnes of fuel oil spilt in the eight days before it could be moved off the rocks and into the port.

More than 200 km of the coast were aff ected by the spill, including many sensitive SSSIs and nature reserves, as oil was washed ashore. Half a million seabirds nest in this area and more than 7000 oiled birds, mainly razorbills and guillemots, were found washed ashore, but it is likely that thousands more were aff ected and died at sea. Many small marine creatures, e.g. limpets and cockles, were killed. Fishing had to be stopped, with some restrictions still in place 18 months later.

Tourism was badly hit because of oiled water and beaches, and parts of the coastal path were closed. Th e loss of revenue was estimated at £2 million in 1996. Th e clean-up operation was thought to have cost £23 million.

Figure 6.27Coastal scenery tbc

Figure 6.28Effects of the Sea Empress oil spill

MilfordHaven

Pembroke

heavyoil

heavyoil

heavyoil

heavy oil

SkomerIsland

SkokholmIsland

The main slick:heavy oil stretchesfor 4 miles

St Ann'sHead

LinneyHead St Govan's

Head

545 badly oiled birds havebeen collected. Dolphinsand porpoises have beenseen swimming in oil inCarmarthen Bay

Key

National Park

Sites of SpecialScientific Interest

Nature Reserve

N

0 50 km

A light sheen of oilstretching acrossCarmarthen Bayto Swansea

Figure 6.29Title: tbc


Annual average watertemperature = 18°C(needed for coral growth)

Coral reefs

Tropic of Cancer

Equator

Tropic of Capricorn

Great Barrier Reef

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6.6 Coral reefs

Most coral reefs are found in warm, tropical waters (Figure 6.30), although there are a small number of cold water corals and some that form in deeper water. Warm, shallow corals need specific conditions in which to form, including:

can thrive

sediment or fresh water

Coral reefs are formed by the skeletons of tiny creatures called polyps. Algae living amongst the coral help it ‘grow’, producing more calcium carbonate. This attracts a huge variety of marine life – coral reefs are often called the ‘rainforests of the sea’ because of their rich biodiversity, thought to be almost one million different species (Figure 6.31). Fish and plants are frequently brightly coloured (Figure 6.31), attracting not only divers and tourists, but also fishermen and those looking to harvest coral to sell.

Figure 6.30

Figure 6.31


Fringing Reef Barrier Reef Atoll

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Marine processes

Formation

a) Fringing reefs form close to the shoreline. Corals attach themselves to submerged land in shallow water and grow upwards to sea level or just below. Fringing reefs are usually quite narrow and don’t have large lagoons separating them from the land.

c) Atolls form when the land sinks below sea level or when sea level rises. They usually form a broken circle around an island. The coral continues to grow upwards and the central, shallow lagoon may become filled with sand and debris broken from the reef.

b) As a fringing reef grows, it becomes further away from the shoreline, creating a large lagoon. As the land/island sinks the reef continues to grow, especially if the water is shallow. Although named ‘barrier’, these reefs are not usually continuous – they are easily damaged and broken up by storms.

Coral reefs start to form when coral attaches itself to submerged land, usually around tropical islands. The coral builds up gradually over time and may change from being a fringing reef (Figure 6.32a and Figure 6.33) to a barrier reef (Figure 6.32b) to an atoll (Figure 6.32c). Eventually they may die and become extinct if the island sinks into deeper water. It could take thousands of years for a reef to complete the entire sequence.

Figure 6.33Fringing reef, Fiji

Figure 6.34Table coral damaged by divers

Figure 6.32The formation of coral reefs


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Coral reefs are unique marine ecosystems but they are also important economically in terms of tourism and fishing. A number of tropical islands such as the Maldives and the Seychelles depend on tourists who visit to see the coral and its teeming wildlife. Many fishing communities rely on the reefs to provide them with a living. As a result of this, and the very precise conditions they need to grow, many of the world’s coral reefs are under threat. A report in 2004 predicted that almost one-quarter of the world’s coral reefs were at high risk of imminent collapse, with another quarter under threat longer term.

The main threats are:

Climate change/global warming: if seas become warmer, algae in the coral will be affected, causing them to lose colour – a process called bleaching. This could kill off all of our coral reefs.

Extreme weather and natural hazards: storms break up and destroy coral. The Asian tsunami in 2004 destroyed large areas of coral in the affected region (p.X, section 3.5).

Pollution: run off from the land takes sediment, chemical waste, sewage and other pollutants into the sea, damaging water quality and corals. Excess CO2 also creates acidification in seas and oceans.

Coastal development: increased human activity along coral coasts increases pollution and fishing. People may also reclaim land from the sea and mine sand and rock from reefs.

Overfishing: pressure to supply local (and global) markets has increased fishing and damage from boats, but also the use of highly damaging methods such as the use of dynamite and cyanide.

Figure 6.35

Coral bleaching factfile

stopped, coral bleaching is set to steadily increase in frequency and intensity all over the world until it occurs annually by

This would devastate coral reefs globally to such an extent that they could be eliminated from most areas of the world by

that reefs could take hundreds of years to recover. The loss of these fragile ecosystems would cost billions of dollars in lost revenue from tourism

as damage to coastal regions that are currently protected by the coral reefs that line most tropical coastlines.

Source: Climate Change and the World’s Coral Reefs, Greenpeace.


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6.7 Coral reefs Case study: The Great Barrier Reef, Australia

Australia’s Great Barrier Reef (Figure 6.36) is the world’s largest coral reef system, stretching for more than 2000 km north to south, between 15 and 150 km off the coast of Queensland. Up to 65 km wide in parts, it covers 345 000 km2. It was declared a UNESCO World Heritage Site in 1981, and is the world’s largest Marine Park.

Great Barrier Reef factfile

Types or species

Coral

Birds

Reptiles

Others Molluscs, dolphins, dugongs, rays, sponges, turtles, humpback whales

N

Far northern section(area: 85 200 sq km)

Cairns section(area: 35 500 sq km)

Central section(area: 76 100 sq km)

Mackay/Capricorn section(area: 143 400 sq km)

Brisbane

Rockhampton

Great Barrier ReefWorld Heritage Area(Area: 348 000 sq km)

Great Barrier ReefMarine Park(Area: 345 000 sq km)

Mackay

Townsville

Cairns

Coral Sea

0 400 km

Figure 6.36The Great Barrier Reef, Australia


Photo 6.39

to come

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Tourism

The marine tourism industry is the largest commercial activity in the Great Barrier Reef region, which is both a World Heritage Site and the world’s largest Marine Park. Visitors contribute more than Aus$5 billion to the Australian economy every year, and the industry provides jobs for more than 50 000 people. There are more than 800 operators and 1500 vessels operating along the reef, ranging from small sailing boats catering for 20 or fewer to luxury catamarans carrying 400 people. Some cruise ships also include it on their itinerary. More than 85 per cent of visitors go ashore in just 10 per cent of the park. Attractions include day, overnight and extended tours, snorkelling, scuba diving and fishing, aircraft or helicopter trips, sailing, cruising and glass-bottomed boat viewing.

Problems

Despite the high numbers of tourists, it is not visitors who pose the real threat to the reef. As is the case for most coral reefs, the main threat is global warming. Coral growth here has declined more in recent years that at any time over the past 400 years. If sea temperatures rise, bleaching could decimate the coral. Deposition of sediment and pollution from the run off of pesticides, fertilizers and detergents from the land are also causing problems.

In terms of wildlife, two species in particular are causing concern. Loggerhead turtle numbers have fallen by 90 per cent in the past 50 years, many getting caught in fishing nets. Dugongs (a large marine mammal) have fared even worse, declining by 97 per cent over the same period, also the victim of fishing nets, but also through hunting or being hit by boats.

Figure 6.37View of the Great Barrier reef, Australia


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Marine processes

6.8 Marine pollutionMost people, even those who live on the coast, see only a small fraction of the marine environment. A significant amount of the pollution that makes its way to our seas and oceans originates on land from human activity. For many years seas and oceans have been treated like giant drains or sewers. Waste finds its way into our rivers, either via our drainage systems (Figure 6.38) or from surface run off, and ultimately into the sea, where tides carry it away from the coast – and out of sight. Waves, tides and currents can carry waste thousands of kilometres away, with some of it washed up along other coastal areas.

44%33%

12%10% 1%

Runoff and discharges from landsewage and industrial waste

Atmospherewind-blown gasesand particles

Marine transportoil spills/leaks,cargo spills

Dumping at seaunwanted waste,ships' garbage

Offshoreproductionwaste from oil/gas production

Figure 6.39 shows the various causes of marine pollution. Sewage and industrial waste have always been discharged into rivers and seas, with large quantities broken down by natural processes. However, we now produce so much that these processes are slowing down. A lot of waste is so toxic or rich in nutrients that algae grow very quickly, blocking out sunlight and reducing oxygen levels in water. This is a real threat to marine ecosystems. The Mediterranean Sea (which is not tidal) has seen great masses of algae in recent years. Swimmers and surfers increasingly suffer viruses and skin complaints through contact with contaminated water.

About three-quarters of marine pollution comes from the land, the rest comes from ships (Figure 6.40), plus a small amount from offshore rigs or platforms. Illegal dumping of waste at sea accounts for an estimated 10 per cent of marine pollution, slightly less than from oil spills or leaks and cargo spills.

Plastic soup

There is an increasing amount of non-biodegradable waste in our seas and oceans, especially plastics. The UN estimates that there are 18 000 pieces of floating plastic for every square kilometre of ocean, and this figure is increasing every year.

About 20 years ago a huge amount of rubbish was discovered in the North Pacific Ocean, thousands of kilometres from land. Few commercial ships sail here as the seas are nutrient-poor with only small numbers of fish and marine life.

Figure 6.40Ships account for nearly a quarter of marine pollution

Figure 6.38Waste being discharged into water course

Figure 6.39Causes of marine pollution


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There are now two separate areas of what is now called ‘plastic soup’ around the Hawaiian Islands (Figure 6.41), known as the Eastern and Western Pacific Garbage Patches or Trash Vortex. The reason that plastic soup has collected here in the North Pacific Gyre is because the current spirals clockwise, taking rubbish from countries around the Pacific Rim with it. About 10 per cent of the plastic we manufacture every year (10 million tonnes) ends up in the oceans. This includes plastic goods such as containers, fishing nets, polystyrene and a whole range of smaller objects such as plastic bags and bottles. Some is washed up onto beaches, but a larger proportion slowly breaks down into smaller pieces. Industry also provides an important ingredient for the soup in the form of tiny plastic pellets used to make many of our plastic products, washed into rivers from factories and eventually to the sea.

Plastic soup does not biodegrade. It floats as a mass just on or below the surface of the water. Most of it cannot be seen from the air because it is translucent. These could damage existing habitats as alien species. Plastic soup mixes with plankton, the base of the marine food chain. Small marine mammals and birds feed on the plankton, swallowing plastic soup at the same time. Albatrosses (Figure 6.42) mistake some of the rubbish for squid and ingest it and feed it to their chicks. More than 1 million seabirds and 100 000 marine mammals die every year from swallowing plastic or becoming entangled in it and drowning. It provides a route for living organisms to be transported around the globe. There are also fears that under certain conditions plastics may release highly concentrated toxins and that this may move right through the food chain.

Oy a s h

i o C

ur r e n t

A l a s k a C u r r e n t

K u r o s h i o C u r r e n t

N o r t h E q u a t o r i a l C u r r e n t

E q u a t o r i a l C o u n t e r C u r r e n t

Ca

l i f or

nia

Cu

rrent

E A S T E R NG A R B A G E

P A T C H

Hawaii

W E S T E R NG A R B A G E

P A T C H

0 500 1000 kilometres

Figure 6.41

Figure 6.42Albatrosses frequently ingest large quantities of plastic, mistaking it for food


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Marine processes

Summary

understand the action of waves and how they erode, remove, transport and deposit material around coastlines

describe the differences between constructive and destructive waves and how this affects swash and backwash

identify and explain the formation and location of a range of coastal landforms including cliffs, wave-cut platforms, caves, arches, stacks, headlands and bays, beaches, spits, bars, sand dunes and salt marsh.

attrition, hard and soft engineering methods

describe and explain the process longshore drift

describe the different measures used to manage coastal areas, including different hard and soft engineering methods

explain how coastal areas have to be managed to serve a range of users

describe the different types of coral reefs and the conditions under which they are formed

list the causes of marine pollution and the problems created

where appropriate use relevant case studies and a range of maps, data and statistics


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Activities

(ii) The feature described in (b)(i) is designed to help prevent coastal erosion – in particular erosion via longshore drift. Explain how it works. (4)

c) Describe how a headland may be eroded to form a series of features, culminating in a stack and

Softer rock

WA

VE

S

Softer rock

Harder rock

Resistant (harder) rock

Less resistant(softer) rock

(ii) Beaches are stores of sediment/rock material. Where does this material come from and how does

Figure 6.43


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Marine processes

Figure 6.44Waves approaching the coast at an angle. TBC

Figure 6.45One problem caused by human activity to a coral reef

(ii) Describe the sequence of events that leads to the formation of an atoll. (4)

as coral reefs. For a named area of coral reef you have studied, describe the main threats caused by


140

Give one example of each type (other than those shown in (a)(iii) and (b)(i)), describing the main

d) For a named coastal area you have studied, describe how it is managed to satisfy different needs

b) (i) (ii) What natural and human actions have caused the formation of the areas called the Eastern

Figure 6.47Coastal defences

Figure 6.46Managing coastal erosion


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