OS34B-01 INVITED
Engineered Carbon Storage in the Oceans
The amount of carbon in the ocean is large relative to the amount of fossil-fuel resources. The oceans are currently absorbing over 8 billion tons of anthropogenic carbon dioxide each year and will eventually absorb most anthropogenic carbon dioxide emissions. These observations have led many to ask whether it might be helpful to engineer an acceleration of this transfer of carbon to the oceans, and, if so, to understand how this feat might be accomplished most economically and with a minimum of adverse environmental consequence. There is no unique taxonomy of engineered ocean carbon storage options, but they might broadly be divided into three categories, depending on whether they depend for their efficacy primarily upon physics, chemistry, or biology. Physics. Carbon dioxide could be captured from power plants and injected deep in the ocean, where physical mixing processes could keep it isolated from the atmosphere for centuries. Sub-species of this category include injection of carbon dioxide directly into the deep ocean, into seafloor lakes, or into engineered containment vessels. Chemistry. Alkalinity, derived from limestone or other minerals, could be added to the ocean, causing carbon to be stored effectively permanently in the oceans primarily in the form of bicarbonate ions. Sub- species of this category include the dissolution of calcium carbon at power plants or in deep-waters near upwelling zones. Biology. Some of the organic matter sinking from the surface ocean to the deep ocean is replaced by carbon dioxide from the atmosphere. Thus, it has been proposed that we should attempt to diminish atmospheric carbon dioxide concentrations by fertilizing the oceans. Sub-species of this category include fertilization with micronutrients such as iron or macronutrients such as nitrogen or phosphorus. This talk will present this taxonomy and quantitatively discuss some of the pros and cons and unanswered research questions associated with each approach.
OS34B-02
Electrocemical Production of Ocean Alkalinity for Carbon Dioxide and Acid Mitigation, and Hydrogen Generation
Various schemes have been proposed to increase air-to-sea CO2 transfer and storage, including the addition of alkalinity to the ocean. Examples include the addition of: Ca(OH)2 derived from the thermal calcination of limestone (Kheshgi, 1995), NaOH from the electrochemical splitting of salt (House et al., 2007), and CaCO3 to carbonate-undersaturated waters (Harvey, 2008). Diluted in the ocean (to pH<9) such alkalinity would react with dissolved CO2 to form primarily dissolved mineral bicarbonates. Another alternative would be to generate Ca(OH)2 directly in seawater via electrochemically forced dissolution of CaCO3. Using DC current of appropriate voltage, protons generated by a water-splitting anode submerged in seawater could be used to chemically decompose otherwise insoluble limestone leading to formation of Ca(OH)2 and thus chemical enhancement of CO2 absorption by the ocean. In turn, H2 gas produced at the cathode could be used to recover/store energy, helping defray process costs. Chlorine generation might be avoided via the use of certain current densities, or the use of oxygen- selective anodes, the net reaction then being: CaCO3+CO2+2H2O---DC--- >1/2O2+H2+Ca(HCO3)2aq. Laboratory experiments showed that such a system can generate excess alkalinity and elevated pH in seawater that subsequently allowed the absorption of 0.8 mM atmospheric CO2. Thus at larger scales, wind-, wave-, or solar-powered, fixed/floating platforms at the shoreline, in coastal waters, or in the open ocean might be employed to electrochemically increase ocean alkalinity. Such platforms would then: 1) enhance the ocean's natural absorption of atmospheric CO2, 2) help neutralize or offset the effects of ongoing ocean acidification, via the calcium hydroxide and/or bicarbonate production, and 3) generate carbon-negative H2 in the ratio 22kg CO2 absorbed/kg H2 produced.
OS34B-03
Estimation of Turbulent Diffusion of Carbon Dioxide by Small-scale Eddies in the Deep Ocean by Low-wavenumber Forcing
Turbulent diffusion of carbon dioxide was estimated by using the numerically-generated small-scale eddy field by the low-wavenumber forcing. We estimated the temporal and spatial information of velocity field by the spectral analysis of four sets of time series measured simultaneously at different points in the deep ocean. The estimated velocity information was forced into the large-eddy simulation as the low-wavenumber (larger than the domain size) components in order to generate high-wavenumber (smaller than the domain size) components. This nonlinear operation usually results in the overestimation of the energy at the high wavenumbers since the low wavenumbers generated by the interaction of the forced low wavenumber and the high wavenumbers cannot be resolved by the conventional FFT filter. This overestimation of the energy also brings about the large energy dissipation, leading to the inaccuracy in the estimation of the turbulent diffusion. In order to avoid this problem, a new spectral filter which can treat the wavenumbers, the corresponding lengths of which are not always the multiple of domain length, was introduced. By using this filter, the generated low wavenumbers are removed properly from the computational domain, and the energy spectrum follows the -5/3 power law. Finally, the diffusion of the carbon dioxide was simulated in the reproduced eddy field and its characteristics were estimated.
OS34B-04
Conceptual Approaches to Testing the Efficiency and Impact of Ocean Iron Fertilization (OIF) for Enhancing CO2 Storage in the Ocean
Recent experiments to determine the efficiency of carbon sequestration during natural and artificially stimulated phytoplankton blooms suggest that bloom events can transfer as much as 50% of the new phytoplankton production to depths below 500 m. Such efficiencies would make OIF a cost-effective mechanism for CO2 mitigation. In order to further quantify sequestration and to determine its impact on the ocean environment, the scientific community has proposed larger (up to 200 × 200 km) OIF experiments and has suggested that they be monitored for longer periods of time than previous experiments (up to 70 days). In addition, new technologies for measurement and more sophisticated modeling to both design the experiment and project its impact have been proposed. We will report on a proposed project conceptual design for such an experiment.
OS34B-05
Sequestering Naturally Occurring Liquid Carbon Dioxide in the Deep Ocean
Liquid carbon dioxide has been found as shallow as 1,500 meters in seafloor ooze. Did the liquid carbon
dioxide originate from volcanic activity? Or did bacteria convert organic matter, which started as atmospheric
carbon dioxide, into methane and liquid carbon dioxide? At typical ocean temperatures carbon dioxide
coming out of solution below 600 meters will be liquid. Therefore, one likely mechanism for generating liquid
carbon dioxide in seafloor ooze is the bacterial decomposition of organic matter. This paper examines
quantitative and qualitative bacterial decomposition of aquatic biomass, with an emphasis on assessing and
demonstrating feasibility.
Calculations suggest natural processes sequestering liquid carbon dioxide in the seafloor can be sustainably
increased to decrease atmospheric carbon dioxide concentrations. First, algae growing on the ocean
surface absorb carbon dioxide. The algae are then gathered into a submerged container. Naturally
occurring bacteria will digest the algae producing methane, liquid carbon dioxide, and ammonium. The
ammonium can be recycled as a nutrient for growing more algae.
Bacterial decomposition continues in dilute solutions with any biomass. The process does not require any
particular biomass. Also, concentrating the biomass by removing water is not essential. The buoyancy
provided by water allows relatively inexpensive tension fabric structures to contain the dilute algae and
decomposition products. Calculations based on algae growth in open ponds and experience with bacterial
decomposition at 1 to 5 bar pressures suggest the economics of the associated macro-algae growing and
harvesting can favor increasing ocean species diversity.
http://www.PODenergy.org
OS34B-06
Environmental Assessment for Potential Impacts of Ocean CO2 Storage on Marine Biogeochemical Cycles
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.
OS34B-07
Sources of Nutrients for Ocean Enrichment
The remarkable doubling of the productivity of the land over the last 50 years raises the question of
opportunities to follow suit in the sea. The rapidly rising population makes increasing demands on food
supply and the disposal of waste in the atmosphere from fossil fuel burning
It is well known that the supply of nutrients to the photic zone of the ocean limits primary production and this
limitation can be removed by the addition of nutrients. The surface waters of the ocean are typically in the
photic zone for a decade and their initial quota of nutrients are supplemented by cyanobacteria, atmospheric
deposition and river inflows. Together with upwelling these nutrients support about 10,000GtC of new primary
production per year.
Extra nutrients can be sourced from the thermocline, from enhancing the diazotrophs or by chemically
transforming elements on the land or in the atmosphere. Using thermocline nutrients to enhance productivity
but are first order neutral for carbon sequestration. Diazotrophs seem restricted to temperate and tropical
waters and need phosphate and other nutrients. The increased nitrogen they provide is expected to lead to
more carbon storage in the ocean. The macronutrients, nitrogen and phosphorus and the micronutrients
have all been shown to be beneficial. With increased new primary production we expect increased
sustainable fish production but the species composition will depend on the success of recruitment.
http://www.otg.usyd.edu.au