CO2 Capture and Storage
6. Could CO2 be stored in the deep ocean?
- 6.1 What are the methods of ocean storage?
- 6.2 What are possible environmental impacts and costs of ocean storage
6.1 What are the methods of ocean storage?
is soluble in water, there are
natural exchanges between the atmosphere and the surface of the ocean
that occur until a balance is reached. If the atmospheric
concentration of CO2 increases, the oceans are
expected to take up additional CO2 gradually over
several centuries until a new equilibrium is reached. The
CO2 would first be dissolved in the upper ocean layer
and later be mixed with deep ocean waters. In this way, the
oceans have taken up about 500 GtCO2 of the total 1
300 GtCO2 released by human activities into the
atmosphere over the past 200 years. Oceans are currently taking
up about 7 GtCO2 per year. Most of this carbon
dioxide now resides in the upper ocean layer which has become
somewhat more acidic as a
result (a decrease of 0.1 in
pH). To date, however, there
has been virtually no change in acidity in the deep
be injected directly into the deep ocean, where
most of it would be isolated from the
atmosphere for centuries.
This could be achieved by transporting CO2 via
pipelines or ships to an ocean storage site, where it would be
injected into the water column of the ocean or at the sea floor.
The dissolved and dispersed CO2 would then become
part of the global
carbon cycle. Ideas for
storing CO2 away in the deep ocean for even longer
periods of time include forming solid CO2 hydrates
and/or liquid CO2 lakes on the sea floor, and
dissolving alkaline minerals
such as limestone to neutralize the
6.2 What are possible environmental impacts and costs of ocean storage
can be injected into the deep ocean from oil
Source: Stephen Knowles
The injection of a few GtCO2 would produce a
measurable change in ocean chemistry in the region of injection,
whereas the injection of hundreds of GtCO2 would
eventually produce measurable changes over the entire ocean
volume. Over centuries, ocean mixing would result in a gradual
into the atmosphere.
Experiments have shown that the addition of CO2 can
harm marine organisms close to injection points or
CO2 lakes. Long term effects of direct CO2
injection on large ocean areas have not yet been studied. It is,
however, expected that
impacts on ocean ecosystems
would increase with increasing CO2 concentrations and
decreasing pH, and it is
unclear how or whether
species and ecosystems
would adapt to the chemical changes.
The cost of ocean storage has been estimated
based on the cost of offshore pipelines or ships, plus any
additional energy costs at 6 to 31
net injected. For short distances (100 km offshore), the fixed
pipeline option would be cheaper. For larger distances (500 km
offshore), injection from a moving ship or transport by ship to
a platform with subsequent injection would be more attractive.
The global and regional treaties on the law of the sea and
marine environment, such as the
OSPAR and the
London Convention, also
concern ocean storage, but the legal status of intentional ocean
storage has not yet been decided.
Storage in oceans would thus be a less environmentally
acceptable and a more expensive storage option for
In the few public perception studies conducted so far, the
public has expressed greater reservations about ocean storage
than geological storage.
Note from the editor: Because of its environmental implications, CO2 storage in oceans is generally no longer considered as an acceptable option.