OCEAN

ACIDIFICATION

Kajal Kamble

MBT- I

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

•Definition :-

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.

CARBON CYCLE

•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),

bicarbonate (HCO−3) and

carbonate (CO2−3).

•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.

ACIDIFICATION

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

concentration).

CO2 (aq) + H2O <-> H2CO3 <-

> HCO3− + H+ <-> CO3

2− + 2

H+

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.

CALCIFICATION :-

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

shells.

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

MARINE ORGANISMS

Shellfish:-

o Thinner, smaller and weaker shells in

shellfish

o Especially larval stages, which already have

thin shells.

o Fitness effect: Lower survival due to

increased crushing and drilling by

predators.

Coral:-

Ocean acidification could compromise the

successful fertilization in coral.

• Deformed flagellum in sperm that

impacts their swimming

• Fitness effect: lower population

growth

Norma

l

Acidi

c

Reall

y

acidic

Ocean acidification: Impacts on individual

marine organisms

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

will decline

Ocean acidification: Impacts on individual marine organisms

Amount of dissolved carbon

Lots Little Lots Little

Ph

oto

syn

the

sis

Gro

wth

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:

1. Tolerate

2. Adapt

3. Move

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.

Sea urchin

Normal Acidic

Cool water

Warm water

Hot water

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

Total extinction• A distinct possibility if ocean acidification continues.

Present

First

modern

corals

Million years ago

High

coral

growth

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.

REFERENCES :-

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

organisms“.

Web sites

www.google.com

www.wikipedia.com

THANK YOU