As in coral bleaching, where if the harsh

As majority of the Great Barrier Reef coastline is
low-lying, rising sea levels has a
significant impact. Sea levels have started to rise by approximately 3mm per
year since 1991 (Australian Government: Great Barrier Reef Marine Park Authority,
2017). This is due to thermal expansion in
the oceans and glaciers melting. This current sea level change is very, however,
there are beliefs that sea levels have remained almost entirely constant for
the past 6000 years, this results in a well-defined depth profile across the
reefs.

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Climate change has caused rising sea surface temperatures. This is
already affecting the Great Barrier Reef but it does have a high potential to
create significant effects across the whole ecosystem. Within limited
temperature ranges corals have been able
to evolve over thousands of years, but corals are put under thermal stress with
these limits being exceeded. This causes the coral to expel the tiny algae
(zooxanthellae) that live within their
tissues. Zooxanthellae is what gives corals their colour and most of their food and energy. This then results in
coral bleaching, where if the harsh conditions do not ease within a couple of
weeks the coral will eventually starve and die. 

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This is because the calcification rate is decreased and the coral will
have to compete with the newer coral that also requires calcium
carbonate. 

The term calcification means the speed at
which a coral’s calcium carbonate skeleton is deposited. There have been
reports over the years of coral growth rates slowing. The cause of this can be
due to ocean acidification. As carbon dioxide is absorbed from the atmosphere
by the ocean, it bonds with the seawater
to form carbonic acid. The carbonic acid then releases a bicarbonate ion and a
hydrogen ion. The hydrogen ion will the bond with a free carbonate ion to form
another bicarbonate ion. That free carbonate ion would have been otherwise
available to marine life to create calcium carbonate shells and skeletons. This
means that the more carbon dioxide dissolved into the ocean, the less free
carbonate ions for making calcium carbonate. The increase in ocean acidity decreases the ability for
coral to build their skeletons, which then means that it decreases their
ability to create habitats for other marine life that lives on the reef. It
also means that the reef struggles to repair itself after physical erosion and
biological erosion.

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The ocean has been estimated to have absorbed approximately half of the
excess CO2 released by human activity (anthropogenic CO2) in the past 200
years. This is resulting in chemical changes in the oceans. This chemical
change is in the oceanic pH level decreasing by 0.1 to gain more acidity,
although it will still remain alkaline (ocean acidification). From a current pH
of 8.2, it is predicted that the ocean’s pH level will drop to 7.8 by
2100. 

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Carbon
dioxide is released into the atmosphere through either natural or human
activity. Natural causes include plant and animal respiration, soil respiration
and decomposition, ocean-atmosphere exchange, and volcanic eruptions. Some
of the human activities that cause CO2 emissions include the burning of fossil
fuels (coal, natural gas, and oil),
deforestation and electricity and heat generation. CO2 emissions are one of the most major causes of global
warming which has a significant impact on the Great Barrier Reef. Global
warming has contributed to a growing amount of negative impacts. These include
ocean acidification, change in sea temperature and rising sea levels. 

sub intro- 

The destruction of the Great Barrier Reef has been caused by several
human impacts. One of these being the release of CO2 emissions due to human
activities, such as the burning of fossil fuels. This causes the ocean to be
subject to effects of ocean acidification. CO2 emissions contribute greatly to
global warming which is a very significant cause of the destruction of the Great Barrier Reef.