WO2008124883A1

WO2008124883A1 - Method of determining the amount of carbon dioxide sequestered into the ocean as a result of ocean nourishment

Info

Publication number: WO2008124883A1
Application number: PCT/AU2008/000528
Authority: WO
Inventors: Ian Jones
Original assignee: Ocean Nourishment Corporation Pty Limited
Priority date: 2007-04-17
Filing date: 2008-04-15
Publication date: 2008-10-23
Also published as: AU2008238614B2; AU2008238614A1; AU2007201687A1

Abstract

A method for measuring the removal of carbon from a designated zone of the ocean to the deep ocean, responsive to the addition of nutrients to the designated zone, is disclosed. The method comprises the steps of: (a) determining the direction and speed of a current flow across a plane that extends through the designated zone; (b) determining an average temperature along the plane; (c) determining an average chlorophyll concentration along the plane; (d) estimating from the chlorophyll concentration and temperature, the concentration of inorganic carbon converted to organic carbon, as a result of the addition of nutrients, over the area of the plane; and (e) determining a product of the current flow and the concentration of converted organic carbon over the plane to provide a measure of the flux of inorganic carbon converted and removed from the designated zone and, from the integral of this with respect to area, determining the total flux across the plane to yield a value of carbon removed from the designated zone to the deep ocean.

Description

Method for Determining the Amount of Carbon Dioxide Sequestered into the Ocean as a Result of Ocean Nourishment

Technical Field

5 A method for measuring the amount of carbon dioxide sequestered into the ocean from the atmosphere is disclosed. More particularly, the method can be used for measuring the amount of carbon removed from the upper ocean as a result of the introduction thereto of nutrients.

0 Background Art

The CO₂ concentration in the atmosphere has been rising, primarily as a result of fossil fuel burning. The United Nations Framework Convention on Climate Change (UNFCCC) indicates that there is a need to reduce the CO₂ content of the atmosphere for climate and food security. In addition, the Framework acknowledges that poor 5 nations are likely to suffer the most from rapid climate change. At the same time, the fishing industry is arguably exploiting the ocean's food resources beyond its generating capacity.

The natural process by which carbon dioxide is converted into organic carbon is known. When atmospheric carbon dioxide dissolves in the ocean it exists in an ionic O form and is taken into the bodies of marine phytoplankton through the process of photosynthesis, and is converted into an organic form.

A process of increased photosynthesis in the ocean may address both increased atmospheric carbon dioxide and depleted food resources by increasing the conversion of inorganic carbon (carbon dioxide) to organic carbon (phytoplankton vegetable matter). 5 Such vegetable matter may then form the basis of the marine food chain.

The phytoplankton produced by this conversion eventually perish through age or are eaten by other marine organisms. The resulting dead or excreted biomass then falls to lower levels in the ocean. In this regard, a phenomenon is known whereby organic carbon sinks from the surface ocean to the deep ocean (occurring over most of O the ocean) and a compensatory flux of carbon from the deep ocean to the surface occurs by upwelling and diffusion. In addition, it is known that inorganic carbon in the surface ocean is in communication with the carbon dioxide in the atmosphere. When carbon stored in the deep ocean is supplied by the atmosphere, the process is termed carbon dioxide sequestration. Related sequestration methods in this respect are disclosed in US5992089, and by Jones (1996) in "Enhanced carbon dioxide uptake by the world's ocean" (Energy Convers. & Mgmt, 37, 1049-1052) and Jones and Young (1997) "Engineering a large sustainable world fishery." {Environmental Conservation, 24, 99-104).

Whilst some of the organic carbon material is promptly exported to the deeper ocean, some is converted to inorganic material in the surface ocean. The recently converted inorganic material can be used by a next generation of phytoplankton to form a new standing stock of organic material. This process represents a secondary production of organic material. This cycling of carbon in and out of the organic state eventually leads to all the carbon initially converted to organic material to be exported from the surface ocean to the deeper ocean.

Li some regions of the ocean, however, the conversion of carbon dioxide dissolved at the surface of the ocean to organic carbon during the sunlit periods is limited by the availability of specific nutrients, for example, the macronutrient nitrogen or the micronutrient iron.

A process of nourishing the ocean can be used to increase the mass of carbon in transit in the deep ocean by providing nutrients that are in short supply to increase photosynthesis and thereby convert a greater amount of inorganic carbon (carbon dioxide) to organic carbon.

Methods are known that involve the addition of nutrients such as nitrogen or iron to a body of water in order to sequester carbon dioxide from the atmosphere and provide an effective carbon sink. Nitrogen is also continually supplied to the surface ocean by natural processes and its first conversion to organic matter represents a primary production of organic material. The steady state nature of the reactive nitrogen concentration in the surface ocean indicates that all the inorganic carbon converted to organic material is eventually exported from the ocean surface layer. In addition, the references made in this Background to prior art documents do not represent an admission that the documents form a part of the common general knowledge of a person of ordinary skill in the art in Australia or elsewhere . Summary of the Disclosure

It has been surprisingly discovered that changes in carbon dioxide content of the upper ocean can be determined using biological indicators of the conversion of inorganic carbon to organic carbon and the fact that such converted carbon is exported to the deep ocean.

Therefore, in one aspect there is disclosed a method for measuring the removal of carbon from a designated zone of the ocean to the deep ocean, responsive to the addition of nutrients to the designated zone, the method comprising the steps of: (a) determining the direction and speed of a current flow across a plane that extends through the designated zone;

(b) determining an average temperature along the plane;

(c) determining an average chlorophyll concentration along the plane;

(d) estimating from the chlorophyll concentration and temperature, the concentration of inorganic carbon converted to organic carbon, as a result of the addition of nutrients, over the area of the plane; and

(e) determining a product of the current flow and the concentration of converted organic carbon over the plane to provide a measure of the flux of inorganic carbon converted and removed from the designated zone and, from the integral of this with respect to area, determining the total flux across the plane to yield a value of carbon removed from the designated zone to the deep ocean.

Such a method can determine the amount of inorganic carbon converted and exported to the deep ocean whereby a process of nourishing the ocean to increase carbon dioxide sequestration can then provide a tradeable carbon credit, hi addition, previously it has not been recognised that promoting the conversion of inorganic carbon to organic carbon is sufficient to ensure export of carbon from the surface ocean, or that its promotion and measurement can thus provide a tradeable commodity.

The term "designated zone" typically comprises the surface layer of the ocean In turn, the term "surface layer" usually refers to the zone of ocean above the so-called thermocline. Further, the term "thermocline" usually refers to a layer of the ocean, below the surface ocean, where the change of density gradient is large.

The designated zone typically comprises the surface layer because a number of properties of the surface layer can be approximated as constant with depth. When considering such terminology, it is to be appreciated that oceans are divided into numerous regions depending on the physical and biological conditions of these areas. For example, the pelagic zone includes all open ocean regions, and can be subdivided into further regions categorised by depth and light abundance. The photic zone typically covers the ocean from surface level to 200 metres down. The aphotic zone typically covers all depths exceeding 200m. A further discussion on the different ocean zones is provided at the end of the Detailed Description.

Thus, it is to be appreciated that the terms "designated zone" and "deep ocean" are to be broadly interpreted. hi one example, the designated zone can comprise the so-called photic zone, but it may comprise deeper or shallower zones.

The term "deep ocean" is understood by a person of ordinary skill in the art to lie beneath the surface layer, typically in deep regions of the so-called aphotic zone.

The term "nutrient" is used in this specification to refer to one or more substances that promote the growth of phytoplankton, such as nitrogen, phosphorous and iron.

The terminology "flux" refers to the amount of substance that flows across a unit area.

In the method, the plane does not pre-exist in the ocean in a physical sense; rather, it is determined (or decided upon) in practice of the method. For example, it can be determined as extending generally transversely (eg. perpendicularly) to a current flow in the designated zone. The plane can also extend generally vertically. In addition, the plane is typically located away from a point of nutrient addition, usually in a region of the designated zone where the limiting nutrient had just been exhausted. In step (d), the conversion to organic carbon can be determined using the following equation: conversion of carbon = Chl/(0.003+A x exp(0.05T) = R x ChI where T is the average water temperature (measured in degrees Centigrade), ChI is the average chlorophyll concentration, and A is the temperature coefficient and can be specified to equal 0.006 or a locally determined value. For example, A can be determined from in-situ measurements to relate organic carbon to ChI at a known temperature. R is the ratio of carbon weight to chlorophyll weight of a naturally occurring assemblage of phytoplankton and can be determined by measurement. Thus, ChI can be used as a marker for export of carbon from the surface ocean. In step (b), the average temperature can be determined by measuring the temperature at a number of depths in the designated zone along the plane. hi step (c), the average chlorophyll concentration can be determined by measuring the chlorophyll concentration temperature at a number of depths in the designated zone along the plane. Further, in step (c) the average of chlorophyll over depth can be determined from a measurement of a water leaving radiance and the depth of the designated zone.

The depth of the designated zone can be measured or it can be determined from a numerical ocean model.

Again, in step (a) the current flow can be measured or it can be determined from a numerical model.

In step (e), the total flux across the plane can be derived from the sum of all the fluxes integrated over depth along the plane. In another aspect there is disclosed a method of producing a tradeable carbon credit comprising the steps of:

(i) determining the amount of inorganic carbon converted and exported to the deep ocean responsive to the addition of nutrients to a designated zone of the ocean using a method as defined in the first aspect; and (ii) equating the converted amount from (i) to an amount of carbon dioxide sequestered by the ocean to in turn provide the tradeable carbon credit.

Detailed Description of Specific Embodiments

When nutrients are added (eg. injected) into a moving ocean current of low productivity, the inorganic carbon (carbon dioxide) starts to be converted immediately to organic carbon. In the present method this represented new primary production.

This process continued as the nutrients were swept downstream, until all of at least one critical nutrient was fully consumed. The amount of organic carbon produced was then determined by estimating the flux of organic material (away from the point of nutrient injection) through a plane that was generally (or "roughly") perpendicular to the local flow.

Example 1 A photic zone in the temperate ocean was designated as the zone for measurement of carbon removed from the zone responsive to nutrient introduction. The organic carbon flux was defined as the concentration of organic carbon multiplied by the current in the zone. When the concentration was measured in gm/m³ and the current in m/s, the flux was in gm/m²s.

A vertical plane was established in the zone away from a point of nutrient (in this case nitrogen and phosphorous) injection. When the selected plane was too close or too far from the injection point, the final flux of organic carbon from the introduction of nutrient was underestimated. The optimal position of the plane was observed to be in a region where the limiting nutrient had just been exhausted.

To adjust for any conversion of inorganic to organic carbon in the absence of nutrient injection a so-called background conversion was established. Where the background rate of conversion was known from historical studies to be low, its concentration was either neglected or was set at a value below 0-20% of the measured conversion.

Then, when the increase of organic carbon was greater than a factor 5, the method was able to be practised with sufficient accuracy to enable a tradeable carbon credit to be determined. In this regard, the conversion of inorganic carbon to organic carbon by introduced nourishment was equal to or greater than the difference between the background concentration and the measured organic carbon concentration along the chosen plane. The flux was then calculated with this concentration difference.

The ocean current and the temperature were determined either by direct measurement or, more conveniently, from a numerical model that made use of the equations of fluid motion. It was noted that as the current carried the nutrient "downstream", the amount of chlorophyll increased until the limiting nutrient was nearly exhausted. Thus, it was proposed to use a biological indicator to measure the conversion to organic matter. Chlorophyll concentration thus provided a biological indicator of the amount of organic carbon present in the water. In the case of introduced nourishment the chlorophyll concentration was used to determine the new primary production.

With the aid of equation (1) below chlorophyll concentration was converted to organic carbon concentration. (1) Conversion of carbon = Chl/(0.003+A x exp(0.05T)

where T was the average water temperature (°C), ChI was the average chlorophyll concentration, and A = 0.006 or a locally determined value. The parameters to be determined were temperature and chlorophyll concentration. A number of ways of determining chlorophyll concentration were noted, with three measures being employed, namely, filtration of a sample of water and the estimation of chlorophyll by transmission spectrometry, the use of a fluorometer or the use of water leaving radiance as sensed by a satellite or aircraft. The temperature used in the equation was obtained from satellite, by in situ measurement or from numerical models.

The amount of carbon exported from the surface layer of the ocean as a consequence of nourishment was the total flux of organic carbon created by introduced nourishment integrated over time. The exported carbon was noted to be stored away from the atmosphere for some time.

Example 2

The plane was determined to be 100km downstream of the nutrient injection point. The plane was 20km wide in the horizontal direction. An XBT section with castes at 1 km space was employed to find that the temperature was 19.7 °C ± 0.2 °C in the surface mixed layer. A fluorometer survey was also made on a 1 km spacing down to the base of the mixed layer (as determined by the temperature measurements) at 2 meter depth intervals. The fluorometer readings were converted to chlorophyll concentration using the relationship (confirmed by comparison with spectral determination) based on filtered samples of sea water. At the same time the current speed was determined by an

Acoustic Doppler Current meter, ADC, attached at a survey ship. The results were tabulated as in Table 1 & 2.

Table 1 (at the end of this section) shows Chlorophyll Results (mg/m³) Table 2 (at the end of this section) shows Current (m/s). The procedure was repeated upstream of the injection point and all values of chlorophyll were found to be below 0.5 mg/m³ of chlorophyll. Thus, 0.5 was subtracted from all values in Table 1. Resultant values less than 0 were set to zero.

Next the conversion value of chlorophyll to organic carbon and then carbon dioxide equivalent was found by filtering five samples of local sea water and performing standard chemical analysis (as described in Grasshoff (1999) Methods of Seawater Analysis, Wiley). The value used was 1 gm ChI gave 48 gm of organic carbon gave 48*44/12 gm of CO2 .

The values in Table 1, after conversion to carbon dioxide, were assumed to be representative of a pixel in the plane 2 m x 1000m. From these values the flux of each pixel was determined by multiplying the concentration by the current by the area (2,000m²).

The next step was to determine the total organic carbon flux away from the injection point. The flux in each pixel was summed. In this example, the flux of carbon dioxide had a value of 23gm/second.

The procedure was repeated the following day (day 2). The value of the sum of fluxes was 24 kg/second. The next day it was 23.5 kg/second. Integrating over a day, (1 day =8640 seconds) a typical value for the carbon dioxide sequestered away from the surface ocean by the nutrient addition on day 1 was greater than 2,070 tonnes.

The introduction of nutrients method was termed Ocean Nourishment™ (a trademark of Earth Ocean & Space Pty Ltd). It was observed that the Ocean Nourishment ™ method was able to sequester carbon whilst increasing the sustainable wild fish stocks.

Ocean Zones

As mentioned in the Summary, the ocean is divided into numerous regions depending on the physical and biological conditions of these areas. For example, the pelagic zone includes all open ocean regions, and can be subdivided into further regions categorised by depth and light abundance. The photic zone typically covers the ocean from surface level to 200 metres down. The aphotic zone typically covers all depths exceeding 200m. Then, the pelagic part of the photic zone is known as the epipelagic, whereas the pelagic part of the aphotic zone can be further divided into regions that succeed each other vertically. In this regard, the mesopelagic zone refers to the uppermost region, with its lowermost boundary at a thermocline of 10°C, which, in the tropics generally lies between 700 and 1,000m. Then, there is the bathypelagic zone lying between 10⁰C and 4°C, or between 700 or 1,000m and 2,000 or 4,000m. Lying along the top of the abyssal plain is the abyssalpelagic zone, whose lower boundary lies at about 6,000m. A final zone falls into the oceanic trenches, and is known as the hadalpelagic zone. This lies between 6,000m and 10,000m and is the deepest oceanic zone. Along with pelagic aphotic zones there are also benthic aphotic zones, these correspond to the three deepest zones. The bathyal zone covers the continental slope and the rise down to about 4,000m. The abyssal zone covers the abyssal plains between 4,000 and 6,000m. Lastly, the hadal zone corresponds to the hadalpelagic zone which is found in the oceanic trenches. The pelagic zone can also be split into two subregions, the neritic zone and the oceanic zone. The neritic encompasses the water mass directly above the continental shelves, while the oceanic zone includes all the completely open water. In contrast, the littoral zone covers the region between low and high tide and represents the transitional area between marine and terrestrial conditions. It is also known as the intertidal zone because it is the area where tide level affects the conditions of the region.

In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the method.

Table 1

Station 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Depth

(m) chrlorpyll

02 02 02 02

2 02 02 06 08 08 08 08 08 08 08 08 08 08 08 08 08 03 03 03 03

4 03 03 07 09 09 09 09 09 09 09 09 09 09 09 09 09 03 03 03 03

6 03 03 08 1 1 1 1 1 1 1 1 1 1 1 1 1 03 03 03 03

8 03 05 08 11 11 11 11 11 11 11 11 11 11 11 11 11 03 03 03 03

10 03 06 08 12 12 12 12 12 12 12 12 12 12 12 12 12 03 03 03 03

12 03 08 08 12 12 12 12 12 12 12 12 12 12 12 12 12 03 03 03 03

14 03 09 09 12 12 12 12 12 12 12 12 12 12 12 12 12 03 03 03 03

16 03 09 09 12 12 12 12 12 12 12 12 12 12 12 12 12 03 03 03 03

18 03 1 1 13 13 13 13 13 13 13 13 13 13 13 13 12 03 03 03 03

20 03 1 1 15 15 15 15 15 15 15 15 15 15 15 15 12 03 03 03 03

22 03 1 1 19 19 19 19 19 19 19 19 19 19 19 19 12 03 03 03 03

24 03 1 1 25 25 25 25 25 25 25 25 25 25 25 25 13 03 03 03 03

26 03 1 1 25 25 25 25 25 25 25 25 25 25 25 25 14 03 03 03 03

28 03 1 1 21 21 21 21 21 21 21 21 21 21 21 21 13 03 03 03 03

30 03 09 09 13 13 13 13 13 13 13 13 13 13 13 13 13 03 03 03 03

32 03 09 09 13 13 13 13 13 13 13 13 13 13 13 13 13 03 03 03 03

34 03 09 09 12 12 12 12 12 12 12 12 12 12 12 12 12 03 03 03 03

36 03 09 09 11 11 11 11 11 11 11 11 11 11 11 11 11 03 03 03 03

38 03 06 06 1 1 1 1 1 1 1 1 1 1 1 1 1 03 03 03 03

40 03 06 06 09 09 09 09 09 09 09 09 09 09 09 09 09 03 03 03 03

42 03 06 06 09 09 09 09 09 09 09 09 09 09 09 09 09 03 03 03 03

44 03 03 03 04 04 04 04 04 04 04 04 04 04 04 04 04 03 03 03 03

46 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03

48 03 03 03 02 02 02 02 02 02 02 02 02 02 02 02 02 03 03 03 03 so 03 03 03 02 02 02 02 02 02 02 02 02 02 02 02 02 1 01 01 01 Table 2

Station 1 2 3 4 5 6 7 8 9 10 11 12 13 14 IS 16 17 18 19 20

Depth

(m)

2 04 04 04 04 04 04 04 04 04 04 03 03 03 03 03 03 03 03 03 04

4 04 04 04 04 04 04 04 04 04 04 03 03 03 03 03 03 03 03 03 04

6 04 04 04 04 04 04 04 04 04 04 03 03 03 03 03 03 03 03 03 04

8 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03

10 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03

12 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03

14 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 lό 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02

18 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

20 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

22 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

24 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

26 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

28 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

30 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

32 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

34 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

36 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

38 02 02 02 02 02 03 03 03 03 03 03 03 03 03 03 03 02 02 02 02

40 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02

42 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02

44 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02

46 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02

48 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 so 02 02 01 02 01 02 01 02 02 02 02 02 02 02 02 02 02 02 02 02

Claims

1. A method for measuring the removal of carbon from a designated zone of the ocean to the deep ocean, responsive to the addition of nutrients to the designated zone, the method comprising the steps of: (a) determining the direction and speed of a current flow across a plane that extends through the designated zone;

(b) determining an average temperature along the plane;

(c) determining an average chlorophyll concentration along the plane;

2. A method as claimed in claim 1 wherein the designated zone comprises the surface layer of the ocean.

3. A method as claimed in claim 1 or 2 wherein the plane is determined so as to extend generally vertically and transversely to a current flow in the designated zone.

4. A method as claimed in claim 3 wherein the plane is located away from a point of nutrient addition, in a region of the designated zone where the limiting nutrient had just been exhausted.

5. A method as claimed in any one of the preceding claims wherein, in step (d), the conversion to organic carbon is determined using the following equation: conversion of carbon = Chl/(0.003+A x exp(0.05T) where T is the average water temperature, ChI is the average chlorophyll concentration, and A = 0.006 or a locally determined value.

6. A method as claimed in claim 5 wherein A is determined from in-situ measurements, to relate organic carbon to ChI at a known temperature.

7. A method as claimed in any one of the preceding claims wherein, in step (b), the average temperature is determined by measuring the temperature at a number of depths in the designated zone along the plane.

8. A method as claimed in any one of the preceding claims wherein, in step (c), the average chlorophyll concentration is determined by measuring the chlorophyll concentration temperature at a number of depths in the designated zone along the plane.

9. A method as claimed in claim 8 wherein the average of chlorophyll over depth is determined from a measurement of a water leaving radiance and the depth of the designated zone.

10. A method as claimed in any one of the preceding claims wherein the depth of the designated zone is measured is determined from a numerical ocean model.

11. A method as claimed in any one of the preceding claims wherein, in step (a), the current flow is measured or is determined from a numerical model.

12. A method as claimed in any one of the preceding claims wherein, in step (e), the total flux across the plane is derived from the sum of all the fluxes integrated over depth along the plane.

13. A method of producing a tradeable carbon credit comprising the steps of: (i) determining the amount of inorganic carbon converted and exported to the deep ocean responsive to the addition of nutrients to a designated zone of the ocean using a method as defined in any one of the preceding claims; and

(ii) equating the converted amount from (i) to an amount of carbon dioxide sequestered by the ocean to in turn provide the tradeable carbon credit.