Sequester CO2 in the oceanic dead zones

There are large areas in the ocean which have been rendered anaerobic, presumably by fertilizer runoff. This fertilizer sustains huge algal blooms which then sink, decompose, and in doing so strip all the oxygen from the water. These "deadzones" do not have multicellular life, but are populated by anaerobic bacteria which thrive in the absence of O2. I propose that this situation could be used to sequester and fix CO2.

These zones are already anaerobic, so deterimental effects because of water acidification would not occur. It is probably already fairly acidic. Large regions of these areas might sustain anaerobic bacteria which could fix the CO2 in the absence of light, so one would not need to rely on surface photosyntheic plankton. Also, strategies to increase open ocean CO2 fixation using iron enrichment already run the risk of turning any such stretch of ocean into a dead zone, because of the resulting algal bloom. If the zone is already dead, no further harm would be done!

Finally, it is my hope that CO2 would ultimately be reduced to CH4 in these anaerobic conditions. The methane would form methane clathrates and accumulate on the ocean floor in twining crystalline castles inhabited by worms and crabs. Al Gore would lead tours of these castles using a fleet of small submersibles.