Environmental Impact

 

Environmental impact is one of the chief factors determining the fate of ocean sequestration.  Concern over the change in pH change and carbonate-ion concentration may or may not be legitimate.  It is predicated that adding 200 years worth of carbon dioxide emissions, approximately1300 GtC at the current rate, would decrease the average pH of the ocean by 0.3 units. To put that in perspective, the pH of the ocean has decreased by 0.1 units since pre-industrial times [1] .

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The effects of a change in pH on deep-sea animals are not known.  However, it is probable that whatever the change, in the long run it will be the same whether the carbon dioxide is released into the atmosphere or sequestered in the ocean because so much of the CO₂ in the atmosphere ends up in the ocean eventually. The pH change as a result of immediate sequestration may even be preferable to the natural change because with sequestration, the pH will change in the deep ocean, while the natural change will occur closer to the surface, where there are more marine biota [2] .

 

Monterey Bay Aquarium Research Institute (MBARI) is currently conducting experiments to test the effects of ocean disposal of CO₂ on deep-sea animals. A 2000 study produced the surprising results that deep-sea creatures seemed to be attracted rather than repulsed to a solution with a high concentration of CO₂ that was injected into the ocean.  The scientists have no reached a conclusion as to the reason for this, and further tests will be preformed [3] . However, it is speculated that increased acidity of the ocean will have a negative effect on deep-sea creatures. Deep-sea fish and invertebrates have naturally low metabolic rates, about one-thousandth the rate of surface dwelling creatures [4] , and lowering rate pH of their environs will further inhibit metabolic growth and reproduction [5] .

 

Several studies have also confirmed that a change in pH will have an effect on the surrounding ecosystem.  The extent of the damage done to marine organisms depends on the level of the pH change and length of time the organism was exposed to the change.  For example, after ten hours of exposure to a pH of 5, fish larvae will have a mortality rate of 5, while ten hours of exposure to a pH of 4.5 results in a mortality rate of 9.5.  For small clams, five hundred hours of exposure can either result in a mortality rate of 5 at pH 7 or a mortality rate of 80 at pH 6.  The current sequestering methods, however, are designed to result in a decrease in pH from 8 to at most 7 at the point of injection.  If the injection method is designed so that the CO₂ disperses properly, there should be no pH change at all [6] .

 

Many environmentalists are not pleased with the prospect of ocean sequestration. A scheduled field test by the Pacific International Center for High Technology Research (PICHTR) and sponsored by the U.S. Department of Energy planning sequester 20 tons of CO₂ 4.5 nautical miles off the coast of Nawiliwili, Kauai was cancelled due to large protests by groups such as the Pacific Whale Foundation.  The group cited such concerns as,  "If massive amounts of carbon are dumped into the ocean, how can we be assured that it won't someday rise to the surface and be released into the atmosphere?" and "high CO₂ concentrations are also toxic to marine life." [7]   PICHTR responded that 20 tons of CO₂ is a very small amount, and the pH of the surrounding water would be minimally affected and return to its natural pH within days.  No damage was expected to be done to swimming organisms or the coral reef [8] .

 

There is obviously no general consensus regarding the environmental impact of carbon dioxide sequestration in the deep ocean.  If the pH is expected to change, but by how much and what the impact will be is still inconclusive.