The ocean absorbs about one-third of carbon dioxide emissions from human activities. This uptake benefits society by slowing climate change but causes ocean acidification as CO2 reacts with seawater. Ocean acidification threatens marine organisms that build shells and skeletons, and could disrupt marine food webs and ecosystems. Future projections estimate the oceans will become 150% more acidic by 2100 if emissions continue unabated, reaching levels not seen for over 20 million years. Strengthening the science of ocean acidification impacts is urgently needed to inform decision making.

1. By:
Gayatri R. Kachh

2. • The ocean absorbs a significant portion of carbon dioxide (CO2)
emissions from human activities, equivalent to about onethird of the
total emissions for the past 200 years from fossil fuel combustion,
cement production and landusce change.
• Uptake of CO2 by the ocean benefits society by moderating the rate of
climate change but also causes unprecedented changes to ocean
chemistry, decreasing the pH of the water and leading to a suite of
chemical changes collectively known as ocean acidification.
• The ocean is constantly exchanging with the atmosphere. It stores and
distributes large amounts of heat around the globe via ocean currents.
In this way, the ocean plays a key role for the global climate. However
this regulatory mechanism is presently disturbed by global warming,
consequence of the greenhouse effect.

3. • The carbon cycle involves both organic compounds such
as cellulose and inorganic carbon compounds such as carbon
dioxide and the carbonates. The inorganic compounds are
particularly relevant when discussing ocean acidification for it
includes many forms of dissolved CO2 present in the Earth's
oceans.[When CO2 dissolves, it reacts with water to form a balance
of ionic and non-ionic chemical species: dissolved free carbon
dioxide (CO2), carbonic acid (H2CO3),bicarbonate (HCO
−3
)
and carbonate (CO
−2
3). The ratio of these species depends on
factors such as seawater temperature and alkalinity. These
different forms of dissolved inorganic carbon are transferred from
an ocean's surface to its interior by the ocean's solubility pump.
• The resistance of an area of ocean to absorbing
atmospheric CO2 is known as the Revelle factor.

4. • Ocean acidification is rapidly changing the carbonate system of the world
oceans. Past mass extinction events have been linked to ocean
acidification, and the current rate of change in seawater chemistry is
unprecedented.
• Evidence suggests that these changes will have significant consequences
for marine taxa, particularly those that build skeletons, shells, and tests of
biogenic calcium carbonate.
• Potential changes in species distributions and abundances could
propagate through multiple trophic levels of marine food webs, though
research into the long-term ecosystem impacts of ocean acidification is in
its infancy.
• Many marine organisms form biogenic calcium carbonate including:
crustose coralline algae (the primary cementer that makes coral reef
formation possible), Halimeda (macroalgae), foraminifera,
coccolithophores, tropical reef-building corals, cold-water corals,
bryozoans, mollusks, and echinoderms. The majority of marine calcifiers
tested to date are sensitive to changes in carbonate saturation state and
have shown declines in calcification rates in laboratory and mesocosm
studies.
Impact On Marine Ecosystem

7. • Since the beginning of the Industrial Revolution, the pH of surface ocean waters has
fallen by 0.1 pH units. Since the pH scale, like the Richter scale, is logarithmic, this
change represents approximately a 30 percent increase in acidity. Future predictions
indicate that the oceans will continue to absorb carbon dioxide and become even
more acidic.
• Estimates of future carbon dioxide levels, based on business as usual emission
scenarios, indicate that by the end of this century the surface waters of the ocean
could be nearly 150 percent more acidic, resulting in a pH that the oceans haven’t
experienced for more than 20 million years.

9. Ocean acidification is an emerging global problem. Over the last decade, there
has been much focus in the ocean science community on studying the
potential impacts of ocean acidification. Since sustained efforts to monitor
ocean acidification worldwide are only beginning, it is currently impossible to
predict exactly how ocean acidification impacts will cascade throughout the
marine food chain and affect the overall structure of marine ecosystems. With
the pace of ocean acidification accelerating, scientists, resource managers,
and policymakers recognize the urgent need to strengthen the science as a
basis for sound decision making and action.