(The Gist of Science Reporter) Turning Ocean Waters Acidic Threatening Marine Life [APRIL-2020]
(The Gist of Science Reporter)
Turning Ocean Waters Acidic Threatening Marine Life
Turning Ocean Waters Acidic Threatening
Seawater to be alkaline. Yet, our oceans are becoming more and more
acidic. In fact, they are currently 26% more acidic is salty, and as such
one would expect it than they were before the world became industrialized,
with the rate of acidification increasing faster than we have ever witnessed
Atmospheric Carbon Dioxide (CO2) continues to rise due to anthropogenic
CO2 emissions which are released when fossil fuels are burned.
This CO2 doesn’t just waft away into space, some of it remains in the
atmosphere where it acts as a greenhouse gas that traps heat, making the
planet warmer; and about 30% of it is absorbed by the oceans, where it
changes the chemistry of seawater, making it more acidic.
Yet, while this does reduce the amount of carbon dioxide in the
atmosphere — which is currently 40% higher than it was before the industrial
revolution — it is the primary cause of ocean acidification.
There are two other potential causes of acidification:
Acidification of coastal waters due to runoff containing nitrogen and
phosphates from land-based sources;
Release of carbon stored in frozen methane hydrates found in the ocean
sediments, which can potentially be released due to ocean warming — a
process that would not be reversible.
Oceans Act as Carbon Sink:
The oceans play a key role in the natural carbon cycle, with carbon
dioxide moving from the atmosphere into the oceans across the
As carbon dioxide is found in higher concentrations in the atmosphere,
it is readily absorbed by the oceans, which traditionally act as a carbon
When carbon dioxide dissolves in seawater it enters the carbonate system
where it occurs in one of three forms: dissolved carbon dioxide, carbonate
ions (CO32−) or bicarbonate ions (HCO3−).
When carbon dioxide is absorbed into the oceans from the atmosphere it
can chemically react with seawater to form carbonic acid (H2CO3), which
slowly releases hydrogen ions (H+). Some of these hydrogen ions bond with
carbonate ions present in seawater to form bicarbonate.
Consequently, as more and more carbon dioxide is absorbed by the oceans,
the concentration of carbonate decreases while the concentrations of
hydrogen and bicarbonate increase, resulting in a decrease in pH (potential
of hydrogen — the scale used to measure the concentration of hydrogen).
The more hydrogen ions are present in seawater (or any solution), the
more acidic it is, and therefore the lower the pH.
Effects of Ocean Acidification:
Impact on Marine Life: Dissolved carbon dioxide is assimilated by
phytoplankton during the process of photosynthesis, and carbonate ions
(calcium carbonate, CaCO3) are synthesized by zooplankton and other marine
organisms, such as snails, shellfish and corals to build shells and
While high concentrations of CO2 may be beneficial to photosynthesizing
phytoplankton, fleshy algae and seagrasses if sunlight and nutrients are
freely available, it can be detrimental to other marine life.
Carbonic acid can reduce the concentration of calcium carbonate needed
by zooplankton and other calcium builders to build and maintain their shells
This can affect development, growth, and survival of a wide range of
species – from tiny zooplankton to mollusks, coral, urchins and to a lesser
degree, even crustaceans such as crabs.
Coral reefs provide essential ecosystem services: they provide food and
shelter for a wide range of marine species and are important breeding
habitat and nursery grounds for commercial fishery species.
They also offer coastal protection from storm surges and are an
important source of tourism revenue.
Their demise would have substantial ecosystem, economic and social
Impact on Marine Ecosystems: With some species, such as
phytoplankton and seagrass expected to fare better in acidic waters than
others, we are likely to see shifts in the species composition of various
This will lead to changes in food webs, where predators will have to
find alternative food sources in order to survive. Those that are unable to
adapt are likely to disappear.
Impact on Society: With severe implications to marine food webs,
ocean acidification ultimately poses a severe threat to ecosystem health and
diversity and to both subsistence and commercial fisheries, as well as coral
The demise of these income-generating sectors could have substantial
social and economic ramifications.
A number of mitigating solutions have been proposed to reduce ocean
Reducing CO2 Emissions: As anthropogenic CO2 emissions are the
primary cause of ocean acidification, the most realistic and feasible
mitigation solution is to reduce the amount of CO2 in the atmosphere by
reducing CO2 emissions. To achieve this, we ultimately need to reduce the
amount of fossil fuels that are burned to produce power.
Removing CO2 from the Atmosphere: While removing CO2 from the
atmosphere using geoengineering methods seems a tad far-fetched and is
likely to be expensive, it can easily be accomplished naturally by
implementing appropriate land use practices that promote the absorption of
atmospheric CO2 by plants and soil — for example, tree planting initiatives,
reforestation, and wetland restoration programs.
Reducing Coastal Pollution: Reducing nutrient pollution of
coastal zones could be an important mitigation measure in areas where
pollution from terrestrial sources is a key driver of acidification. This is
particularly relevant in areas where calcifying marine organisms contribute
significantly to the local economy, for example, coral reef tourism or
Improving Ecosystem Resilience: While building ecosystem
resilience in itself will not reduce ocean acidification, mechanisms such as
marine protected areas can serve as tools to help ecosystems become more
resilient to the impacts of ocean acidification and other stressors.
Using Additives: The addition of alkaline mineral rocks to the
ocean to act as a buffering agent to reduce acidity, as has been used in
freshwater lakes, would only be economically feasible and effective in
coastal areas on a small scale. Scaling this up for the entire ocean would
simply not be effective; nor would it be economically viable. This option
could potentially have negative environmental impacts that are still
Adapting Human Activities: Human activities that depend on the
oceans, such as commercial aquaculture and fisheries, may need to adapt to
changes in ocean acidity as our knowledge and understanding improve through
research. This may lead to affected industries evolving in line with changes
and impacts if they wish to survive. For example, hatchery managers can farm
species that have a higher tolerance of acidification, they can relocate
their operation, or they can limit pumping of water into tanks/ponds when pH
levels are not too low.
Reducing Atmospheric Warming: Reducing other greenhouse gases and
using geoengineering methods, such as solar irradiation, that target
atmospheric warming rather than atmospheric CO2 are not likely to be
beneficial in the short term. However, they may play a role over larger time
scales by preventing carbon stored in methane hydrates from being released
into the oceans due to melting hydrates.
While some of the above solutions are indeed creative, the only truly
feasible and effective way to reduce atmospheric CO2 and ultimately ocean
acidification is to reduce the amount of CO2 emitted into the atmosphere in
the first place. The most effective way to do this would be to replace dirty
fossil fuels with cleaner sources of energy. The technology is available, we
just need the political will to push ahead with this.