Process for sequestering into the ocean the atmospheric greenhouse gas carbon dioxide by means of supplementing the ocean with ammonia or salts thereof

The present invention provides a method for removing CO.sub.2 from the atmosphere. The method comprises the step of delivering a source of nitrogen to the mixed layer of the ocean to cause an increase in the number of phytoplankton in the mixed layer and thereby increase the amount of photosynthesis carried out by the phytoplankton. The source of nitrogen is delivered to the mixed layer at a location where an ocean current will carry the source of nitrogen and phytoplankton over a region of the ocean having a depth sufficient to allow dead phytoplankton and organic material derived from the phytoplankton to fall from the mixed layer and enable carbon originating from the CO.sub.2 to be sequestered from the atmosphere.

FIELD OF THE INVENTION 
The present invention relates to a method for removing carbon dioxide from 
the atmosphere. More particularly, the method of the present invention 
involves delivering an exogenous source of nitrogen to a specific layer of 
the ocean at a specific location to stimulate the growth of the 
phytoplankton population in the specific layer and so cause an increase in 
the photosynthetic activity of the phytoplankton population. 
BACKGROUND OF THE INVENTION 
It is generally agreed under the United Nations Framework Convention on 
Climate Change (FCCC) that there is a need to reduce the CO.sub.2 content 
of the atmosphere. The present invention may enhance the global 
environment by slowing potentially harmful changes to the climate due to 
increases in atmospheric CO.sub.2, a so-called greenhouse gas. The method 
may allow CO.sub.2 to be removed from the atmosphere for centuries and 
increase fish stocks for consumption by peoples of developing countries. 
Cost efficient fossil fuel may therefore be burnt while their by-product, 
CO.sub.2, is put to use rather than dumped into the atmosphere. 
The natural process by which carbon dioxide present in the ocean is 
sequestered is known. (Andersen, N. R. and A. Malahoff, 1977: The fate of 
fossil fuel CO.sub.2 in the ocean. Plenum Press, N.Y., 749pp.). When 
atmospheric carbon dioxide dissolves in the ocean it exists in an ionic 
form and is taken into the bodies of marine phytoplankton through the 
process of photosynthesis. The phytoplankton eventually perish through age 
or are grazed by zooplankton. The resulting dead or excreted biomass then 
falls to lower levels of the water column where it is broken down by 
bacteria which re-release the carbon into the water column. However, 
typically 10% of the biomass escapes bacterial decomposition and falls to 
the ocean depths thereby effectively sequestering the carbon from the 
atmosphere. 
It has been speculated that about 20% of ocean surface waters are deficient 
in trace nutrients required for phytoplankton growth. Martin et al 
(Nature, Vol. 371, pgs. 123-128) observed an increase in phytoplankton 
populations when iron was added to the sea surface in areas where 
phytoplankton numbers were low. 
SUMMARY OF THE PRESENT INVENTION 
In contrast to the above mentioned prior art the present invention teaches 
that phytoplankton populations can be increased by adding a source of 
nitrogen to the mixed layer of the ocean and that by delivering the source 
of nitrogen to a specific location of the ocean the phytoplankton 
population can be utilised to decrease the atmospheric CO.sub.2 
concentration. 
In a first aspect of the present invention there is provided a method for 
removing CO.sub.2 from the atmosphere comprising the step of delivering a 
source of nitrogen to the mixed layer of the ocean to cause an increase in 
the number of phytoplankton in the mixed layer and thereby increase the 
amount of photosynthesis carried out in the mixed layer by the 
phytoplankton, wherein the source of nitrogen is delivered to the mixed 
layer at a location where ocean currents will carry the source of nitrogen 
and phytoplankton to a region of the ocean having a depth sufficient to 
allow dead said phytoplankton and organic material derived from the 
phytoplankton to fall from the mixed layer and enable carbon from the 
CO.sub.2 to be sequestered from the atmosphere. 
As CO.sub.2 present in the mixed layer of the ocean is used in 
photosynthesis carried out by the phytoplankton further CO.sub.2 diffuses 
into the mixed layer from the atmosphere. Accordingly, the addition of the 
source of nitrogen to the mixed layer enhances the function of the ocean 
as a sink for carbon dioxide and results in a reduction in the carbon 
dioxide concentration in the atmosphere. 
The phrase "source of nitrogen" will be understood to mean a nitrogen 
containing compound or compounds which can be used by the phytoplankton. 
The phrase "mixed layer of the ocean" wherever used in the specification is 
to be taken to mean the upper layer of the ocean which is penetrated by 
sunlight and which is subject to mixing by the atmosphere. 
The phrase "ocean currents" will be understood to include a current at the 
selected location of the ocean which is capable of directly carrying the 
source of nitrogen and phytoplankton to the region of the ocean. The 
phrase will also be understood to include situations where at least one or 
more currents at or in the vicinity of the selected location act to carry 
the nitrogen and phytoplankton to a second location where a prevailing 
current then moves the source of nitrogen and phytoplankton to the region 
of the ocean. 
Typically, the mixed layer extends from the surface of the ocean to a depth 
of about 50 meters. However, the mixed layer may extend to a depth of 100 
meters or more. The actual depth of the mixed layer varies and is 
dependent upon a number of factors including wind strength and the 
temperature difference between the oceanic surface waters and the lower 
atmosphere. 
In embodiments of the present invention the source of nitrogen used is 
ammonia or one of its salts. While it is preferable that the ammonia is in 
solution, ammonia in the gas phase may also be utilised in the invention. 
Ammonia occurs naturally in sea water as a result of the bacterial decay 
of dead phytoplankton or zooplankton excretions. 
However, other sources of nitrogen may be used in the present invention 
such as sodium nitrate and nitric acid. 
In preferred embodiments the source of nitrogen is pumped into the mixed 
layer through a pipeline. Typically, the concentration of the source of 
nitrogen pumped into the mixed layer is such that the concentration of 
nitrogen in the vicinity of the pipeline outlet is raised between about 10 
to 60 .mu.g per liter of seawater. The actual concentration of the source 
of nitrogen in the pipeline depends on the strength of the ocean current 
at the pipeline outlet. 
Typically, the region of the ocean to which the ocean currents carry the 
source of nitrogen and phytoplankton is about 1000 meters deep or greater. 
It is an advantage that a method embodied by the present invention causes 
the removal of CO.sub.2 from the atmosphere and results in carbon from the 
CO.sub.2 being locked away in the deep ocean from the atmosphere for 
significantly long periods of time. 
By increasing phytoplankton numbers through the presence of the added 
source of nitrogen ocean fish stocks may be enhanced.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
FIG. 1 illustrates a land based pumping station 1 for pumping ammonia in 
solution through a pipeline 2 into the mixed layer of the ocean at a 
selected location. An ocean current at the selected location carries the 
ammonia and phytoplankton consuming the ammonia to a region of the ocean 
characterised by having a sea-bed 3 at a depth of about 1000 meters or 
more. Preferably, sea-bed 3 is at a depth of at least 1500 meters. 
Alternatively, the source of nitrogen may be pumped through a pipeline by a 
pump arranged in the pipeline itself. Moreover, the source of nitrogen may 
be supplied from land or from a platform anchored at sea. 
Pipeline 2 may be up to 50 km, 100 km, 200 km or greater in length. The 
actual length of pipeline 2 depends on the distance of pumping station 1 
from a suitable ocean current. Preferably, the outlet of the pipeline is 
located close to the edge of continental shelf 4. One example of a 
possible location for the outlet of the pipeline is off Smoky Cape, New 
South Wales, Australia (approx. latitude 30.degree. S). However, there are 
of course other locations which are suitable for carrying out the present 
invention. 
The ammonia solution is pumped through substantially vertical riser pipe 5 
which extends into the mixed layer of the ocean. The addition of the 
ammonia to the mixed layer raises the concentration of nitrogen in the 
vicinity of the outlet of riser pipe 5 about 35 .mu.g per liter of 
seawater. This concentration is below levels which occur sporadically in 
the upper ocean due to upwelling events. 
Preferably, the ammonia solution is released into the mixed layer through a 
plurality of riser pipes 5 which may be spaced apart from each other by a 
distance of up to 1000 meters or more. The respective riser pipes 5 may 
also be arranged so that the ammonia solution is released into the mixed 
layer at different depths. 
Each riser pipe 5 may be provided with a flexible joint allowing an upper 
section of the pipe to move in the unlikely event of being inadvertently 
struck by a passing vessel. 
Preferably, a diffuser 6 is connected to the upper end of riser pipe 5 to 
facilitate the dispersion of the ammonia into the mixed layer. One example 
of a suitable diffuser 6 is illustrated in FIG. 2. Diffuser 6 consists of 
a tubular member having a sealed end 7 and a plurality of holes 8 through 
which the ammonia exits into the mixed layer. The ammonia enters diffuser 
6 through an opposite end which is connected to riser pipe 5. 
Flotation devices may be connected to diffuser 6 or to the upper end 
section of the riser pipe 5 to maintain riser pipe 5 substantially 
vertical. For example, diffuser 6 illustrated in FIG. 2 is provided with a 
flotation collar 9. However, it will be appreciated by the skilled 
addressee that it is not necessary that riser pipe 5 be held in a 
substantially vertical position. 
As depicted in FIG. 1 the ammonia is released into the mixed layer away 
from immediate contact with the atmosphere. Typically, the ammonia 
solution is released at a depth of about 35 meters. 
However, ammonia may be added to the mixed layer by bubbling gaseous 
ammonia from an outlet located beneath the mixed layer of the ocean. 
Alternatively, ammonia in solution may be sprinkled onto the mixed layer 
from an outlet positioned above the surface of the ocean. 
The released ammonia forms a nutrient plume 10 which is transported by the 
ocean current over sea-bed 3. Eddy currents and diffusion assist in the 
dispersion of the ammonia through the mixed layer. 
The presence of the added ammonia together with sunlight enable the 
phytoplankton in the mixed layer to multiply as the ammonia is consumed. 
Dead phytoplankton and organic material comprising excretion from 
zooplankton subsequently fall to lower levels of the water column as 
organic detritus 11 as the ocean current carries the ammonia and 
phytoplankton over sea-bed 3. 
The organic detritus 11 carries with it carbon originating from CO.sub.2 
from the atmosphere enabling effective sequestering of the carbon to 
deeper ocean layers or sea-bed 3. 
Although the present invention has been described hereinbefore with 
reference to several embodiments, numerous variants and modifications are 
possible without departing from the scope of the invention which is 
defined in the following claims.