Manipulation of the Oceanic Carbon Sink

As we saw earlier (Sabine and Feely, Chapter 3, this volume), the oceans constitute an enormous sink for CO2 and have buffered much of the anthropogenic CO2 added to the atmosphere since the industrial revolution. The big uncertainties still to be addressed by scientists hinge on quantifying just how much CO2 the oceans are actually taking up and on how they will respond to a warming planet. Currently, we can estimate the ocean uptake of CO2 by the concentration of chlorophyll in the surface waters as recorded from satellites. This gives great coverage, but unfortunately the amount of CO2 taken up by the phyto-plankton in the surface waters of the oceans is not always directly related to the amount of chlorophyll - the phytoplankton change the ratio of carbon to chlorophyll depending on their depth and supply of nutrients. A big challenge, then, is to better link the

Fig. 16.1. Enhanced oil recovery by CO2 injection. (1) Carbon dioxide (CO2) is injected, along with water, deep underground (1500 m at the Weyburn field) into a depleted oil and gas reservoir. The CO2 used at Weyburn and Midale comes from the Dakota Gasification Plant in Beulah, North Dakota, where the gas is captured (rather than vented to the atmosphere), liquefied by compression and pipelined 320 km north to the oilfields. (2) Oil absorbs CO2, causing the oil to expand. Combined with water injection, CO2 injection increases reservoir pressure and oil fluidity, enabling oil to escape from rock pores and flow more readily towards production wells. (3) Of the injected CO2, ~20% is recycled for enhanced oil recovery and the rest is stored for thousands of years. (From Shawn Griffiths, Petroleum Technology Research Centre, Regina, SK S4S 7J7, Canada. Reproduced with thanks.)

Fig. 16.1. Enhanced oil recovery by CO2 injection. (1) Carbon dioxide (CO2) is injected, along with water, deep underground (1500 m at the Weyburn field) into a depleted oil and gas reservoir. The CO2 used at Weyburn and Midale comes from the Dakota Gasification Plant in Beulah, North Dakota, where the gas is captured (rather than vented to the atmosphere), liquefied by compression and pipelined 320 km north to the oilfields. (2) Oil absorbs CO2, causing the oil to expand. Combined with water injection, CO2 injection increases reservoir pressure and oil fluidity, enabling oil to escape from rock pores and flow more readily towards production wells. (3) Of the injected CO2, ~20% is recycled for enhanced oil recovery and the rest is stored for thousands of years. (From Shawn Griffiths, Petroleum Technology Research Centre, Regina, SK S4S 7J7, Canada. Reproduced with thanks.)

chlorophyll seen by the satellites with the CO2 that is taken up. Regarding the warming of the planet, the extent of increased stratification and so decreased primary production in our oceans remains the ultimate question on oceanic climate change science. With some areas likely to see an increase in storminess, and hence mixing, and others to see a greater predominance of calm high-pressure systems, the weather, as well as sea temperatures, is a key component.

Previous attempts to manipulate the oceanic sink for CO2 have included iron fertilization in the 'high nutrient-low chlorophyll' areas of the world's oceans (e.g. the Equatorial Pacific and the Southern Ocean), where iron appears to be the limiting factor to the growth of phytoplankton. The results of these experiments have been somewhat disappointing, with iron additions resulting in greatly enhanced blooms of phytoplankton, but the bulk of the extra CO2 taken up by these algal blooms being released back into the atmosphere within a relatively short time-span.

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