Submission from the Royal Society of Chemistry
The Royal Society of Chemistry (RSC) welcomes
the opportunity to contribute to the House of Commons Science
and Technology Committee's consultation Investigating the Oceans.
The RSC is the largest organisation in Europe
for advancing the chemical sciences. Supported by a network of
43,000 members worldwide and an internationally acclaimed publishing
business, our activities span education and training, conferences
and science policy, and the promotion of the chemical sciences
to the public.
This document represents the views of the RSC.
The RSC's Royal Charter obliges it to serve the public interest
by acting in an independent advisory capacity, and the RSC is
happy for this submission to be put into the public domain.
Manmade emissions of carbon dioxide
(CO2) are causing the oceans to become more acidic.
To-date, the oceans have absorbed
approximately half of the carbon emitted into the environment
The ability of the oceans to continue
to absorb carbon dioxide is not well understood; current carbon
levels and changes in global temperatures may have a significant
Increasing carbon acidity could have
a significant impact on many marine organisms, specifically calcifying
organisms and larger aquatic animals. The effects of ocean acidification
on these, and other organisms, is not completely known.
The deep oceans have been suggested
as potential storage sites for carbon.
Much research is needed before the
viability of deep ocean carbon storage can be evaluated. The effect
of such schemes on the oceans, at a local and global scale, and
on deep ocean life has not been determined.
The Royal Society of Chemistry is concerned
about the impact of human activity on oceanic ecosystems. One
of the foremost problems is the acidification of the oceans. This
arises as a result of increased carbon dioxide (CO2) absorption
by the oceans as a direct result of an increase in atmospheric
CO2 levels caused by human activity such as the combustion of
fossil fuels, agriculture, deforestation and cement production.
The deep oceans have also been suggested as
a suitable environment for storing carbon dioxide as a means to
mitigate climate change. Many of the scientific questions regarding
this are also closely associated with the absorption of carbon
dioxide by the oceans and its subsequent acidification.
The RSC fully endorses the 2005 report by the
Royal Society entitled "Ocean acidification due to increasing
atmospheric carbon dioxide" in its scientific evaluation
of ocean acidification, its discussion of related socio-economic
impacts, and its recommendations for future research and governance.1
The issue of oceanic acidification has also been discussed by
the Intergovernmental Panel on Climate Change (IPCC) in its 2001
Climate Change report.2 The following section highlights some
key aspects of ocean acidification.
There is now wide-spread acceptance that carbon
dioxide (CO2) released into the atmosphere through human activities
is having a negative impact on global climate. Since pre-industrial
times the atmospheric level of carbon dioxide has risen from about
280 ppm to about 380 ppm today, and it is still rising. This increase
in atmospheric CO2 levels does not account for all manmade carbon
emissions; over half of total CO2 emissions produced in the last
200 years have been absorbed by the oceans.3
The concentration of carbon dioxide (CO2) in
the oceans directly correlates to that in the atmosphere. When
atmospheric CO2 levels rise then there is a concurrent increase
in that absorbed by the oceans. When CO2 dissolves in the oceans
it combines with water to form carbonic acid, H2CO3, which in
turn dissociates to form carbonate ions, HCO3-, and hydrogen ions,
H+. Further ionisation of HCO3- leads to the formation of carbonate
ions, CO32-, and H+. It is the generation of hydrogen ions, or
protons, that leads to the lowering of oceanic pH, ie the ocean
becomes more acidic. The composition of dissolved inorganic carbon
(DIC) in the ocean typically comprises aqueous CO2 (1%, including
H2CO3), bicarbonate ions (3%) and carbonate ions (CO32-, 8%).
These ratios will vary according to local conditions including,
primarily, temperature and up- welling of CO2-rich deep water.
Over the past 200 years the average pH of the oceans has dropped
by 0.1 pH units (a 30% increase in H+).
The oceans act as a carbonate buffer, which
has, to date, been highly beneficial to mankind in minimising
damage ocean acidification caused by high levels of CO2 emissions.
The decrease in ocean pH is therefore less than would be expected
for the quantity of CO2 absorbed. However, as increasingly large
amounts of CO2 become absorbed in the oceans then their ability
to act as a buffer is lessened.
Currently the quantity of CO2 absorbed by the
oceans per year is two Gt (Gt = gigatonne; one Gt = 109 tonnes).
For comparison, a fully laden supertanker weighs approximately
250,000 tonnes. As oceanic carbon dioxide levels increase, this
rate of absorption will drop. Increases in average global temperature
will potentially lead to increased vertical stratification (decreased
mixing), thus decreasing the amount of CO2 that can be absorbed
(it may also decrease the flow of nutrients). If CO2 emissions
continue as at present then the pH of the oceans is predicted
to drop by approximately 0.5 units by 2,100, corresponding to
a three fold increase in H+ ions since pre-industrial times. Importantly,
reversing current changes in ocean pH could take tens of thousands
of years, ie it is essentially irreversible in our lifetimes.
This is because oceanic mixing between surface and deep waters,
which is required in order to bring up ocean sediments to buffer
acidity changes, is a very slow process.
There is the potential for ocean acidification
to have a significant impact on aquatic life. The greatest detrimental
effect may be felt by those organisms that produce structures
made from calcium carbonate (CaCO3). Calcifying organisms include
molluscs, corals, echinoderms, foraminifera and calcareous algae.
The calcium carbonate produced by these organisms is used in external
and internal structures, and in one of two forms: calcite or aragonite.
Crucially, calcium carbonate will dissolve into seawater if the
surrounding concentration of carbonate ions (CO32-) is not high
enough. It also becomes more soluble at lower ocean depths as
a result of decreasing temperature and increasing pressure. A
"saturation horizon" can therefore be defined; in waters
above this depth CaCO3 does not dissolve but below this depth
it does. Currently calcifying marine organisms live above the
saturation horizon, however, lowering the pH of seawater will
result in a decrease in the concentration of CO32- and the saturation
horizon will be elevated closer to the ocean surface. Aragonite
is more soluble than calcite, and its saturation horizon is closer
to the ocean surface than it is for calcite.
The acidification of the oceans may also have
an impact on non-calcifying organisms. Most photosynthetic organisms,
such as phytoplankton, obtain inorganic carbon from dissolved
CO2 or bicarbonate ions. As it is an active process then increases
in dissolved inorganic carbon is likely to have only a small effect
on photosynthesis and, in turn, on growth rates. The effect of
increasing dissolved carbon concentrations on non-photosynthetic
organisms is less well-understood, although it is anticipated
that they will respond to increased CO2 concentrations.
Larger oceanic animals may also be adversely
affected by increased CO2 concentrations. The respiratory system
of such animals relies on obtaining oxygen from water, in which
it is present in only very low levels. This is also accompanied
by removal of CO2, to a much lower level than that required by
land mammals. Large aquatic, water breathing mammals are therefore
highly sensitive to the concentration of carbon dioxide in the
oceans; increased CO2 can lead to acidification of bodily tissues
There is also some concern that ocean acidification
will have a direct impact on the availability of nutrients and
the presence of toxins in the aqueous environment. The modification
of ocean chemistry could have significant impacts on sea life.
In the oceans metals can either be in complexed or free dissolved
forms; the latter is considered to be toxic. Decreasing the pH
of the oceans is anticipated to result in an increase in the concentration
of free metals. Predicting the impact of this change is highly
problematic though, with the role of trace elements in aquatic
biochemical processes still an area of ongoing research.
Key questions that may need to be addressed
How will CO2 absorption by the oceans
be affected in the future by current absorption and by increased
Do climate change models need to
be addressed with regards to changes in rates of CO2 absorption?
To what extent will calcifying organisms
be affected at current CO2 levels and at future projected levels?
What research needs to done to identify
the effects of ocean acidification on non-calcifying organisms?
How will ocean acidification affect
the ratio of complexed to freely dissolved metals in the oceans,
and what impact will this have on aquatic organisms?
What effect will ocean acidification
have on the availability (concentration, speciation etc) of nutrients
such as phosphates, silicates and ammonium ions.
Will the corrosion of ship hulls
be adversely affected by increased ocean acidity?
Carbon capture and storage has been proposed
as a means to decrease the quantity of carbon dioxide emitted
by human activities, thus helping minimise the impact on global
climate. Using deep oceans as repositories for carbon dioxide
has been proposed and a detailed study of this concept has been
carried out by the IPCC and is included in their Special Report
Carbon dioxide Capture and Storage.4
The two main concepts include "dissolution",
in which CO2 is injected at depths of 1,000 m or more and the
CO2 subsequently dissolves, or by "lake" deposition
in which CO2 is injected onto the sea floor at depths of greater
than 3,000 m where it is anticipated that, being denser than water,
it would form a lake and dissolution would be delayed.5 Both schemes
rely upon the slow mixing of ocean water of differing depths.
There is general agreement that carbon stored
by this method would remain isolated for several hundreds of years,
although not permanently. Fractions stored at greater depths will
be retained for longer periods of time, and this can be extended
further by the formation of solid clathrates or liquid CO2 lakes.
The environmental effects of such schemes remain
poorly understood. As dissolution of CO2 progresses the acidity
of the ocean would decrease, as outlined in the previous section.
If the quantity of CO2 injected was limited to only a few Gt then
significant perturbations in ocean chemistry would only occur
locally. Injection of hundreds of GtCO2 would likely result in
measurable changes over the entire ocean volume.
Although life is perceived to be sparse at such
ocean depths, the effects of such high levels of CO2 could have
significant implications for what benthic (floor dwelling) organisms
are present. There are suggestions that such organisms, and deep
ocean microbial populations, may be highly susceptible to changes
in CO2 concentrations and pH.6
A third option is the conversion of carbon dioxide
into bicarbonates or hydrates. This has the potential of minimising
the impact on pH and avoid the need for prior separation of CO2.
However, wider environmental impacts include the use of large
amounts of limestone and the need to require large material volumes.
A final option is to sequester carbon in crop
residue and place large bales of biomass into the alluvial fan
areas of the ocean basin. This could result in rapid burial of
the bales into silt on the sea floor, and therefore the biomass
could be stored for a long time.
Although deep ocean storage of carbon dioxide
must be considered, there are many questions that need answering
in order to be able to judge its viability.7
Is deep ocean storage economically
viable, environmentally safe and socially acceptable?
What are the legal ramifications
of injecting CO2 into the oceans?
How will CO2 interact with water
and ocean sediments at such extreme depths?
What effect will high levels of CO2
have on organisms living on or near the ocean bed?
Will the stratification of the oceans
be affected by current CO2 emission and global warming and what
effect will this have on potential deep ocean storage?
The RSC does not feel that sufficient data exists
presently on this subject. Until these key questions are addressed
satisfactorily then the RSC cannot condone deep ocean storage
REFERENCES 1 Royal
Society, Ocean acidification due to increasing atmospheric
carbon dioxide, 30 June 2005, http://www.royalsoc..ac.uk/document.asp?tip=0&id=3249.
2 IPCC, Climate Change 2001: Impacts, Adaptation
and Vulnerability, Chapter 6 Coastal Zones and Marine Ecosystems.
3 T Takahashi, The Fate of Industrial Carbon
Dioxide, Science, 2004, 305, 352-353.
4 Intergovernmental Panel on Climate Change Special
Report on Carbon dioxide Capture and Storage, Chapter 6
Ocean Storage. http://arch/rivm.nl/env/int/ipcc/pages media/SRCCS-final/IPCCSpecialReport
5 Sea sediment proposed for carbon dioxide, Chemistry
World, August 2006, http://www.rsc.org/chemistryworld/news/2006/August/07080604.asp;
Can we bury our carbon dioxide problem?, RSC Policy Bulletin,
Issue 3, http://www.rsc.org/ScienceAndTechnology/Policy/Bulletins/Issue3/CarbonDioxide.asp.
6 B A Seibel and P J Walsh, Potential impacts
of CO2 Injection on Deep-Sea Biota, Science, 2001,
7 Intergovernmental Oceanographic Commission
of UNESCO, Watching Brief: Ocean Carbon Sequestration.