CO2 dumping by humans:
Ocean Dumping of CO2

We have made it but we don't want it, so what do we do with it? This question could be asked about any number of the byproducts of better living, although the one with which Caldeira and Rau are concerned is anthropogenic carbon dioxide (CO2). They suggest moving CO2 from the atmosphere into the oceans by mimicking the carbonate weathering and dissolution that would occur naturally over thousands of years. Their proposal involves dissolving the CO2 from exhaust gases produced by power plants in seawater, ta make carbonic acid, and then reacting that solution with pulverized carbonate minerals such as limestone to produce a bicarbonate solution that can be released into the ocean. This method would have the advantage of sequestering CO2 as it is made and should cost only one quarter of the projected expense of injecting CO2 directly into the deep sea. Still, this process would require a substantial investment in materials, transportation and infrastructure, and would not remove all of the CO2 produced at a facility. Nevertheless, in combination with other CO2 mitigation strategies, it could reduce significantly the impact of burning fossil fuels.

Geophys. Res Lett. 27. 225 (2000).