The Marine Carbonate SystemCO2 as greenhaouse gas-global warmingOceans regulate the atmospheric CO2 concentrationsWe are in the middle of a global experiment in which several geochemical cycles are being pertubed.

The marine carbonate system represents the largest carbon pool in the atmosphere, biosphere, and ocean and is, therefore, of primary importance for the partition of excess carbon dioxide produced by man. The kinetic processes of exchange and transport are in the area of a few years for the system atmosphere/ mixed surface layer of the ocean, while the exchange time with the deep sea is between 500 and 2000 years. The other important factor controlling the uptake capacity of the oceanic reservoir is the buffer factor, for which recent measurements seem to indicate a necessary revision to lower values (i.e. to a higher buffering capacity). 182 Historical records

Figure 10

www.icsu-scope.org

Figure 11

Reconstruction of Northern Hemisphere temperature anomaly trends from 1000 A.D. to present. From Mann et al

Jerry Mahlman, National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Lab

Maps show the likely ground-level temperature changes in degrees Fahrenheit, if CO2 in the atmosphere doubles its preindustrial levels, then holds for several centuries (top), and if CO2 quadruples its preindustrial levels over 140 years, then holds over several centuries (bottom).MAPS GENERATED BY THE GEOPHYSICAL FLUID DYNAMICS LAB ------------------------------------------------------------------------

Figure 12

In only an hour or so we observed that the volume of liquid dispensed into the two containers was greatly increasing, and that the material dispensed onto the sea floor was swelling or elevating. It became clear that the experiment could not be contained, and soon a series of overflow events occurred, spilling CO2 expelled from the containers onto the ocean floor. We were witnessing for the first time the fluid dynamics of an intense and rapid chemical reaction, with strong motions being generated. The overflow was an Archimedean displacement event, being driven by the incorporation of large volumes of water as a hydrate was formed. This then sank as a dense solid to the bottom of the containers, pushing remaining fluid out the top. Within hours our liquid was converted to a block of ice-like hydrate, imaged standing on the sea floor.

re-analyzed these trajectories incorporating explicit economic considerations for selecting a concentration path. The conclusions are generally recognized as being robust, and were recently adopted by the U.S. Dept. of Energy (7) as a useful target. Figure 2 is taken from this report. It shows one such calculation of the departure required from the IPCC global "Business as Usual" scenario if atmospheric stabilization at about 550 p.p.m.v. (about twice the pre-industrial level) is to be achieved. The numbers are strikingly large; about 1 GtC/year by 2025, and about 4 GtC/year by 2050 are required by the efforts of all nations if the 550 p.p.m.v. target is to be adopted.

To put these numbers in perspective recall that 1 GtC/year was approximately the entire world carbon dioxide output in about 1932, and 4 GtC/year the output of the world in about 1967.

Figure 2. One representation of the reduction in CO2 that would be necessary to reach atmospheric stabilization by comparing the IPCC IS92A ("Business as Usual") scenario with calculations (WRE 550, ref. 6) of emissions trajectories designed to stabilize atmospheric CO2 levels at 550 p.p.m.v. (about twice the pre-industrial level).

For instance Fan et al. (9) claimed that the forests in North America took up 1.4 ± 0.4 GtC/year, as opposed to only 0.1 GtC/year by the forests of Eurasia. Such a large sink is politically attractive to the United States, and would offset completely the continental fossil fuel emissions. But it does not appear to be realistic. Informed comments on this work by others (10, 11) place the true U.S. carbon sink far lower, at perhaps one tenth of this amount. Moreover it is well recognized that carbon storage on land has a strong temporal, rather than permanent, component. Once a forest matures, then carbon is released back to the atmosphere by decomposition and respiration.

Ocean waste disposal option

The injection unit structure design would not only support the valves, associated pipe work and injector nozzles during installation, operation and maintenance but also provide a suitable connection to the seabed and a support for subsea docking of intervention vehicles.

The depth of 500m is well within the range of existing technology and depths approaching 1000m should be achievable without recourse to different technology.

Figure 26

Injecting CO2 at 500m could result in re-entry to the atmosphere within 50 years unless a sufficiently dense plume of CO2-enriched water was produced which could, in the right conditions, sink to greater depths.

The study has indicated that current technology is capable of installing a CO2 injection scheme at l000m which in itself would extend re-entry times significantly.

Figure 27

Check:http://www.ieagreen.org.uk/disp2.htm

Disposal in deep aquifers

The basic principle associated with all subterranean methods of storing CO2 is that it is stored in a geological structure which contains it and prevents short-term or medium term release to the atmosphere.

The structure must consist of a permeable layer, to allow ingress of CO2 and an impermeable or low-permeable layer to prevent escape of CO2 to the atmosphere.

Aquifers are permeable beds, found at various depths and are of variable thickness.

Aquifers are found all over the world but detailed information is generally only available from those areas that are associated with hydrocarbon deposits and where oil and gas exploration work has taken place.

Estimates for potential storage range from 100 GtC to 3000 GtC.

Disposal in exhausted oil and gas reservoirs

The general concept of CO2 disposal in depleted oil and gas wells is that the underground volume of the ultimately recoverable hydrocarbons is replaced by CO2.

To make full use of the storage capacity, the CO2 should be stored as a dense phase fluid i.e. above the supercritical pressure of 7.4MPa and this condition is met at depths below 800m;

About 80% of the world's oilfields are at depths greater than 800m.

The CO2 would be injected and stored in the intergranular pores of the reservoir rock. As dense phase CO2 is still less dense than formation water, it will naturally rise to the top of the reservoir and a trap is required to ensure that it does not reach the surface; this is a natural feature of existing oil and gas wells.

Direct Experiments on the Ocean Disposal of Fossil Fuel CO2

Peter G. Brewer©ˆ, Gernot Friederich©ˆ, Edward T. Peltzer©ˆ & Franklin M. Orr, Jr©˜ .

©ˆ: Monterey Bay Aquarium Research Institute

SCIENCE 284: 943-945 (1999)

transfering liquid CO2 to the accumulator cylinder

Close-up of the accumulator cylinder packed in ice during the filling operation.

A typical ocean water column temperature-pressure profile (solid red line) for Monterey Bay, California overlain on the phase diagram for carbon dioxide in seawater. Depths for three of the experiments are shown for reference.

Phase diagram showing the P-T boundary below which (shaded area in diagram) CO2 injected into sea water forms a solid hydrate. A typical sea water temperature/pressure profile from the ocean off northern California is overlaid. From Brewer et al.

The pressure-density curves for liquid carbon dioxide at various temperatures (solid green line = 10°C, dotted green line = 4°C, dashed blue line = 2°C and solid blue line = 0°C; overlaid on the pressure-density profile (solid magenta line) for seawater at our experimental site. In practice, the neutral bouyancy point for liquid carbon dioxide at 2°C is reached at about 26.50 MPA or approximately 2600 m depth.

Close-up of CO2 gas - hydrate formation at 349 m.

Close-up of CO2 liquid - hydrate formation at 905 m.

deep ocean release apparatus on the bottom at 3627 m. Adding liquid CO2 "dropwise" to the 4L beaker.

Within an hour the liquid CO2 rose to the top of the beaker.

a brightly colored sea-cucumber Peniagone leander

The existence of a thin transparent skin of the hydrate [CO2.6H2O] forms a very strong barrier to CO2 escape, and the animal apparently does not sense any chemical gradient.

A series of frame-grabs of the liquid CO2 spillover from the 4L beaker:

liquid CO2 spillover

Ocean Fertilization

Oceanic phytoplankton. The iron hypothesis. ..based upon demanding laboratory measurements, that truly trace quantities (10-9-10-12M) of iron were lacking. He predicted that addition of trace iron levels to high nutrient-low chlorophyll ocean surface waters would stimulate a phytoplankton bloom, and thus photosynthetically fix carbon, lowering ocean surface CO2 levels, and drawing in atmospheric CO2 by gas exchange in large quantities. A 64 km2 region of the open ocean was induced to yield a doubling of plant biomass, a threefold increase in chlorophyll, and a fourfold increase in plant production, all by the simple and elegant addition of a dilute tracer cloud of iron. The authors of this paper were however obliged to state that "Such experiments are not intended as preliminary steps to climate manipulation". This statement arose from contentious debate well before the experiment was ever executed.

Martin had appeared on national television and uttered the phrase "Give me a tanker of iron and I'll give you an ice age", drawing upon his belief of the role of iron limitation in CO2 changes of climates past.

Uptake by the Ocean. The natural uptake of carbon dioxide from the atmosphere by the ocean occurs on an enormous scale, and the ocean offers the world's most powerful long-term buffer against the rise of both temperature and CO2. Most of the carbon, about 90%, released from the burning of fossil fuels will eventually end up in the ocean. But this will take more than a thousand years to reach equilibrium if the buffering capacity of the carbonate sediments is properly accounted for.

Direct ocean disposal of CO2 was first suggested by Marchetti in 1977

The deep waters of the world ocean are replaced on average every 500 years. The mean replacement time of the Pacific, Indian, and Atlantic Ocean deep waters are approximately 510, 250, and 275 years

The surface ocean today sequesters more than 7 billion metric tons of CO2 per year = 7 GtC/a

The volume of sea water is about 1.37x1021 liters, and the ocean waters contain about 40,000 GtC. The recoverable fossil fuel reserves are about 5,000 to 10,000 GtC, and if about 1,300 GtC were disposed of in the ocean it would on average lower the pH only by about 0.3 units

The transportation and injection costs may be about 15-20% of the total.

The success of the first oceanic iron enrichment experiment lead to a larger and more elegant equatorial Pacific follow-on study in 1995 (25). Here a massive phytoplankton bloom was created in an 8 km x 8km patch through a more careful series of trace iron additions, and a much larger draw down of about 90 p.p.m.v. in ocean surface CO2 levels (Fig. 6) was created (26). The "iron hypothesis" now moved to the status of the "iron theory" and the authors (25) now argued that fluctuations in atmospheric iron deposition on the ocean surface could indeed have created changing atmospheric CO2 levels during glacial periods.

The values of pCO2, NO3, and the fluorescence of chlorophyll across the patch of water fertilized by the trace addition of iron during the IRONEX II study (25). Note the strong removal of nutrients and the draw-down of CO2 caused by the strong growth of phytoplankton. From Millero

www.microscopy-uk.org.uk/. www.si.edu/

Biogenic SedimentsBiogenic sediments, which are defined as containing at least 30% skeletal remains of marine organisms, cover approximately 62% of the deep ocean floor. Clay minerals make up most of the non-biogenic constituents of these sediments.

Distributions and accumulation rates of biogenic oozes in oceanic sediments depend on three major factors: * rates of production of biogenic particles in the surface waters, * dissolution rates of those particles in the water column and after they reach the bottom, and * rates of dilution by terrigenous sediments. The chemistry of deep-sea waters, is, in turn, influenced by the rate of supply of both skeletal and organic remains of organisms from surface waters. It is also heavily dependent upon the rates of deep ocean circulation and the length of time that the bottom water has been accumulating CO2 and other byproducts of biotic activities. Carbonate Oozescoccolith ooze are tiny (less than 10 microns) calcareous plates produced by phytoplankton Foraminiferal ooze is dominated by the tests (shells) of planktic protists belonging to the ForaminiferidaSiliceous OozesBiogenic siliceous oozes have two major contributors. diatoms construct a type of shell called out of opalline silica. Radiolaria also construct opalline silica skeletons.