An in depth summary of A2 Cambridge International A level Geography, notes on coral reefs, including two case studies on wallasea and the great barrier reef
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⑧ BRAAK PHILIP:$ - Coral is a limestone rock made up of skeletons
of tiny marine organisms called coral polyps
- as they die, they leave behind their hard
A CORAL REEF is an accumulation of coral formed skeleton consisting of calcium carbonate which
around the edges of landmasses under certain conditions appears like rock
- they are large underwater structures composed of the - the coral polyps are carnivorous, using
skeletons of colonial marine invertebrates called coral tentacles to sting and kill tiny plankton
- they are a so nourished by tiny plants that live
* ☒MAIL.MN#.**MA.&- within the coral and use sunlight to make food for
the coral
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- 30 degrees N and S of the equator
- eastern sides of land masses ☒A-☒ DANA:*
- border
.
- warm currents - most common shorelines but at a
- salinity between 32 and 42 psu - project seaward directly greater distance
- sea temperature of no less than 21°c from the shore
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- separated from
but optimum is between 23 and 25°c ••☒☒M - form borders along the their adjacent
- maximum 25-40 metres from the sea shoreline and land mass by a
surface as require sunlight for surrounding islands lagoon of open,
photosynthesis often deep water
- clear oxygenated water so need
strong waves ☒iF☒kk
- plentiful supply of microscopic
plankton - if a fringing reef forms around a volcanic island that subsides completely
- not fresh or silt laden water - below sea level while the coral continues to grow upward, an atoll forms
mangroves filter atoned
- atolls are usually circular or oval, with an central lagoon
- found below the low tide mark - parts of the reef platform may emerge as one or more islands, and gaps in the
reef provide access to the central lagoon
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- there are various theories on the formation of atolls
- coral reefs begin to form when free- swimming
coral larvae attach to sunburned rock or other
hard surfaces along the edges of islands or
continents
- as corals grow and expand, reeds take on one
of rheee major characteristic structures - fringing,
barrier or atoll
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REEF FORMATION
Darwin’s subsidence theory to illustrate evolution of three
reed types (South Pacific model), linking the formation of the
three types of reef together
following a rise in sea level or a following even more sea- level
drop I’m the level of the land, a rises, and/or a continued drop in
island surrounded by fringing reefs
barrier reef is formed the level of the land. An atoll is
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barrier reef barrier reef
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Fringing reefs grow around newly If the process is slow the reef will When the island disappears
formed islands. These islands grow upwards to form a larger beneath the sea an atoll forms.
subside, or sea level rises relative battier reef separated from the Coral can continue to grow on the
to land island by a deeper lagoon outside to keep the reef on the
surface. On the inside, where the
land uses to be, quiet water with
increases sedimentation prevails
The origin of fringing reefs is quite clear
- they grow seaward from the land
- barrier reefs and atolls seem to rise from
considerable depth, far below the level at which
coral can grow
- many atolls are isolates in deep water
- the lagoons between the battier and the coast
are usually 45-100 metre in depth and often
many kilometres in width
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