Transport Of Anthropogenic CO2 Research Articles

Variability of the transport of anthropogenic CO<sub>2</sub> at the Greenland–Portugal OVIDE section: controlling mechanisms

Abstract. The interannual to decadal variability in the transport of anthropogenic CO2 (Cant) across the subpolar North Atlantic (SPNA) is investigated, using summer data of the FOUREX and OVIDE high-resolution transoceanic sections, from Greenland to Portugal, occupied six times from 1997 to 2010. The transport of Cant across this section, Tcant hereafter, is northward, with a mean value of 254 ± 29 kmol s−1 over the 1997–2010 period. We find that Tcant undergoes interannual variability, masking any trend different from 0 for this period. In order to understand the mechanisms controlling the variability of Tcant across the SPNA, we propose a new method that quantifies the transport of Cant caused by the diapycnal and isopycnal circulation. The diapycnal component yields a large northward transport of Cant (400 ± 29 kmol s−1) that is partially compensated by a southward transport of Cant caused by the isopycnal component (−171 ± 11 kmol s−1), mainly localized in the Irminger Sea. Most importantly, the diapycnal component is found to be the main driver of the variability of Tcant across the SPNA. Both the Meridional Overturning Circulation (computed in density coordinates, MOCσ) and the Cant increase in the water column have an important effect on the variability of the diapycnal component and of Tcant itself. Based on this analysis, we propose a simplified estimator for the variability of Tcant based on the intensity of the MOCσ and on the difference of Cant between the upper and lower limb of the MOCσ (ΔCant). This estimator shows a good consistency with the diapycnal component of Tcant, and help to disentangle the effect of the variability of both the circulation and the Cant increase on the Tcant variability. We find that ΔCant keeps increasing over the past decade, and it is very likely that the continuous Cant increase in the water masses will cause an increase in Tcant across the SPNA at long timescale. Nevertheless, at the timescale analyzed here (1997–2010), the MOCσ controls the Tcant variability, blurring any Tcant trend. Extrapolating the observed ΔCant increase rate and considering the predicted slow-down of 25% of the MOCσ, Tcant across the SPNA is expected to increase by 430 kmol s−1 during the 21st century. Consequently, an increase in the storage rate of Cant in the SPNA could be envisaged.

Influence of methane and carbon monoxide in the volumetric behaviour of the anthropogenic CO2: Experimental data and modelling in the critical region

Density measurements of the systems CO2+CH4 at T=304.21K and CO2+CO at T=304.21 and 308.15K were carried out at pressures and compositions of interest in the process of transport and storage of CO2 (CCS technology): P=0.1 to 20MPa, and xCO2≥0.97. From the experimental P–ρ–T–xCO2 data, we have studied the dependence of the isothermal compressibility, the excess molar volume, and the partial molar volume of the solute with composition, pressure and temperature within the critical region. We have modelled the volumetric behaviour of these systems with Peng–Robinson, PC-SAFT and GERG Equations of State, thus validating these equations under the conditions considered. Furthermore, we have confirmed the weakly attractive behaviour of these systems by performing a study of the interactions between solvent molecules, CO2, and those of the solute, CO or CH4, using the Krichevskii Function concept and the Kirkwood–Buff Theory. Finally, we have quantified the influence of small amounts of CH4 and CO in the transport of anthropogenic CO2 through several normalized parameters, related to the design and operation of the fluid transport process.

Roles of marginal seas in absorbing and storing fossil fuel CO2

We review data on the absorption of anthropogenic CO2 by Northern Hemisphere marginal seas (Arctic Ocean, Mediterranean Sea, Sea of Okhotsk, and East/Japan Sea) and its transport to adjacent major basins, and consider the susceptibility to recent climatic change of key factors that influence CO2 uptake by these marginal seas. Dynamic overturning circulation is a common feature of these seas, and this effectively absorbs anthropogenic CO2 and transports it from the surface to the interior of the basins. Amongst these seas only the East/Japan Sea has no outflow of intermediate and deep water (containing anthropogenic CO2) to an adjacent major basin; the others are known to be significant sources of intermediate and deep water to the open ocean. Consequently, only the East/Japan Sea retains all the anthropogenic CO2 absorbed during the anthropocene. Investigations of the properties of the water column in these seas have revealed a consistent trend of waning water column ventilation over time, probably because of changes in local atmospheric forcing. This weakening ventilation has resulted in a decrease in transport of anthropogenic CO2 from the surface to the interior of the basins, and to the adjacent open ocean. Ongoing measurements of anthropogenic CO2, other gases and hydrographic parameters in these key marginal seas will provide information on changes in global oceanic CO2 uptake associated with the predicted increasing atmospheric CO2 and future global climate change. We also review the roles of other marginal seas with no active overturning circulation systems in absorbing and storing anthropogenic CO2. The absence of overturning circulation enables anthropogenic CO2 to penetrate only into shallow depths, resulting in less accumulation of anthropogenic CO2 in these basins. As a consequence of their proximity to populated continents, these marginal seas are particularly vulnerable to human-induced perturbations. Maintaining observation programs will make it possible to assess the effects of human-induced changes on the capacity of these seas to uptake and store anthropogenic CO2.

On the variability of atmospheric carbon dioxide concentration at Barrow, Alaska during winter

Winter variability over periods of 1 to 5 days in surface CO2 concentration at Barrow, Alaska was studied by examining the relation between CO2 concentration and air mass. The largest positive anomalies of CO2 concentration occurred with relatively deep surface‐based Arctic air masses. The long residence time in the Arctic of these air masses is qualitatively compatible with both a natural CO2 source, such as the Arctic Ocean, and transport of anthropogenic CO2 from mid‐latitudes in a manner similar to that proposed for the Arctic haze. Trajectories suggest that the anthropogenic CO2 source region of eastern Asia does not contribute significantly to the positive anomalies. The largest negative CO2 anomalies were associated with the influx of air from the North Pacific or North Atlantic regions above a shallow surface‐based Arctic layer. The moisture sounding data suggest mixing or diffusion of this air aloft to the surface through the inversion layer.