The oceans have been absorbing large
amounts of carbon dioxide since the Industrial
Revolution (approximately 1750). It is this increasing
amount of carbon dioxide in the oceans that is
causing ocean acidification
When carbon dioxide (CO2) is absorbed by
seawater, chemical reactions occur that reduce
seawater pH, carbonate ion concentration, and
saturation states of biologically important calcium
carbonate minerals. These chemical reactions are
termed "ocean acidification" or "OA" for short.
•Fluxes of carbon dioxide (CO2) -
oceans, terrestrial biosphere,
lithosphere, and the atmosphere.
•CO2 dissolves - reacts with water -
form dissolved free carbon dioxide
(CO2(aq)), carbonic acid (H2CO3),
•Ratio of these species depends -
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.
Increase in CO2 level - achieve
chemical equilibrium - extra
carbonic acid molecules react
with a water – give bicarbonate
ion, hydronium ion - increasing
ocean "acidity" (H+ ion
CO2 (aq) + H2O <-> H2CO3 <-
− + H+ <-> CO3
2− + 2
THE BIOLOGICAL IMPACTS
Photosynthetic algae and sea grasses may benefit
from higher CO2 conditions in the ocean.
More acidic environment effects calcifying species,
including oysters, clams, sea urchins, shallow water
corals, deep sea corals, and calcareous plankton.
When shelled organisms are at risk, the entire food
web may also be at risk.
Today, more than a billion people worldwide rely on
food from the ocean as their primary source of
protein. Many jobs and economies around the world
depend on the fish and shellfish in our oceans.
Calcium carbonate - building blocks - skeletons and
shells of marine organisms.
Areas where most life now congregates in the ocean,
the seawater is supersaturated with calcium carbonate
minerals causes abundant building blocks for
calcifying organisms to build their skeletons and
Calcification involves the precipitation of dissolved
ions into solid CaCO3 structures, such as coccoliths.
IMPACTS OF OCEAN ACIDIFICATION ON OCEANIC
CALCIFYING ORGANISMS :-
Increased ocean acidity affects marine organisms’ abilities to make and keep
their hard parts.
The more acidic the ocean, the more CO3 reacts with hydrogen, and the
LESS CO3 left for marine organisms to convert into their hard parts.
“Battle” for carbonate!
• Organisms must use more energy or make
less hard part material
• Existing hard parts dissolve (chemical
reaction goes “the wrong way”)
OCEAN ACIDIFICATION: IMPACTS ON INDIVIDUAL
o Thinner, smaller and weaker shells in
o Especially larval stages, which already have
o Fitness effect: Lower survival due to
increased crushing and drilling by
Ocean acidification could compromise the
successful fertilization in coral.
• Deformed flagellum in sperm that
impacts their swimming
• Fitness effect: lower population
Ocean acidification: Impacts on individual
Anemone fish :-
Reduced hearing ability in anemone fish (clown fish) larvae
• Deformed morphology of CaCO3 fish ear bones (otoliths).
• Disruption of acid-base balance in neuro-sensory system.
• Fitness effect: lower survival due to higher predation.
Tropical Oceans Predictions:
• Corals will become increasingly rare
• Algae will become more abundant
• Because coral reefs support so many animals, biodiversity
Ocean acidification: Impacts on individual marine organisms
Amount of dissolved carbon
Lots Little Lots Little
Non-calcifying marine algae: Increased photosynthesis and growth
• Lower pH means more dissolved CO2 for photosynthesis to fuel growth
• Fitness effect: higher survival and population growth
What can be done? Ecological options to OA
• Marine species have 4 possible options:
4. Total extinction
Tolerate the change through acclimatization
• Acclimatize = change phenotype (traits) in response to OA
• Case study: Urchin fertilization
• Eggs have acid-protecting jelly coating.
Move (i.e., shift distribution to non-OA waters)
• In Theory, this is possible because
• Larger animals can swim away
• Larvae can drift away
Adapt (i.e., change genetically over many generations)
• Species would need a fast generation time relative to
rate of pH change.
e.g. California species genetically adapted for OA
• A distinct possibility if ocean acidification continues.
Million years ago
Earth’s two most recent mass extinction events
Both associated with high CO2 levels
OPTIONS TO PREVENT OA
• Reduce fossil fuel emissions
• Support policies to reduce carbon emissions
• Reduce personal carbon footprint.
Iron fertilization :-
Iron fertilization of the ocean could stimulate photosynthesis in phytoplankton.
The phytoplankton would convert the ocean's dissolved carbon dioxide
into carbohydrate and oxygen gas, some of which would sink into the deeper ocean before
oxidizing. More than a dozen open-sea experiments confirmed that adding iron to the
ocean increases photosynthesis in phytoplankton by up to 30 times.
Carbon negative fuels :-
Carbonic acid can be extracted from seawater as carbon dioxide for use in
making synthetic fuel. If the resulting fuel exhaust gas was subject to carbon capture, then
the process would be carbon negative over time, resulting in permanent extraction of
inorganic carbon from seawater and the atmosphere with which seawater is in equilibrium.
Based on the energy requirements, this process was estimated to cost about $50 per
tonne of CO2.
Jacobson, M. Z. (2005). "Studying ocean acidification with
conservative, stable numerical schemes for no equilibrium
air-ocean exchange and ocean equilibrium
chemistry". Journal of Geophysical Research.
James C.; et al. (2005). "Anthropogenic ocean acidification
over the twenty-first century and its impact on calcifying