Environmental Assessment for Potential Impacts of Ocean CO2 Storage on Marine Biogeochemical Cycles
Abstract
Ocean CO2 storage that actively utilizes the ocean potential to dissolve extremely large amounts of CO2 is a useful option with the intent of diminishing atmospheric CO2 concentration. CO2 storage into sub-seabed geological formations is also considered as the option which has been already put to practical reconnaissance in some projects. Direct release of CO2 in the ocean storage and potential CO2 leakage from geological formations into the bottom water can alter carbonate system as well as pH of seawater. It is essential to examine to what direction and extent chemistry change of seawater induced by CO2 can affect the marine environments. Previous studies have shown direct and acute effects by increasing CO2 concentrations on physiology of marine organisms. It is also a serious concern that chemistry change can affect the rates of chemical, biochemical and microbial processes in seawater resulting in significant influences on marine biogeochemical cycles of the bioelements including carbon, nutrients and trace metals. We, AIST, have conducted a series of basic researches to assess the potential impacts of ocean CO2 storage on marine biogeochemical processes including CaCO3 dissolution, and bacterial and enzymatic decomposition of organic matter. By laboratory experiments using a special high pressure apparatus, the improved empirical equation was obtained for CaCO3 dissolution rate in the high CO2 concentrations. Based on the experimentally obtained kinetics with a numerical simulation for a practical scenario of oceanic CO2 sequestration where 50 Mton CO2 per year is continuously injected to 1,000-2,500 m depth within 100 x 333 km area for 30 years, we could illustrate precise 3-D maps for the predicted distributions of the saturation depth of CaCO3, in situ Ω value and CaCO3 dissolution rate in the western North Pacific. The result showed no significant change in the bathypelagic CaCO3 flux due to chemistry change induced by ocean CO2 sequestration. Both bacteria and hydrolytic enzymes are known as the essential promoters for organic matter decomposition in marine ecosystems. Bacterial activity and metabolisms under various CO2 concentrations and pH were examined on total cell abundance, 3H-leucine incorporation rate, and viable cell abundance. Our in vitro experiments demonstrated that acute effect by high CO2 conditions was negligible on the activities of bathypelagic bacteria at pH 7 or higher. However, our results suggested that bacterial assemblage in some organic-rich "microbial hot-spots" in seawater such as organic aggregates sinking particles, exhibited high sensitivity to acidification. Furthermore, it was indicated that CO2 injection seems to be the trigger to alter the microbial community structure between Eubacteria and Archaea. The activities of five types of hydrolytic enzymes showed no significant change with acidification as those observed in the bacterial activity. As to acute effects on microbial and biochemical processes examined by our laboratory studies, no significant influence was exhibited in the simulated ocean CO2 storage on marine biogeochemical cycling. Uncertainties in chronic and large-scale impacts, however, remain and should be addressed for more understanding the potential benefits and risks of the ocean storage.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMOS34B..06Y
- Keywords:
-
- 4805 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 1615;
- 4912);
- 4835 Marine inorganic chemistry (1050);
- 4840 Microbiology and microbial ecology (0465);
- 4899 General or miscellaneous