Revisiting ocean carbon sequestration by direct injection: a global carbon budget perspective

• Published in: Earth System Dynamics
• Main Authors: F. Reith, D. P. Keller, A. Oschlies
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2016
• Subjects: Science; Q; Geology; QE1-996.5; Dynamic and structural geology; QE500-639.5; Southern Ocean
• Online Access: https://doi.org/10.5194/esd-7-797-2016; https://doaj.org/article/f8602a378ecb4e45a51af39009f2b257

In this study we look beyond the previously studied effects of oceanic CO 2 injections on atmospheric and oceanic reservoirs and also account for carbon cycle and climate feedbacks between the atmosphere and the terrestrial biosphere. Considering these additional feedbacks is important since backfluxes from the terrestrial biosphere to the atmosphere in response to reducing atmospheric CO 2 can further offset the targeted reduction. To quantify these dynamics we use an Earth system model of intermediate complexity to simulate direct injection of CO 2 into the deep ocean as a means of emissions mitigation during a high CO 2 emission scenario. In three sets of experiments with different injection depths, we simulate a 100-year injection period of a total of 70 Gt<mspace linebreak="nobreak" width="0.125em"/>C and follow global carbon cycle dynamics over another 900 years. In additional parameter perturbation runs, we varied the default terrestrial photosynthesis CO 2 fertilization parameterization by ±50 % in order to test the sensitivity of this uncertain carbon cycle feedback to the targeted atmospheric carbon reduction through direct CO 2 injections. Simulated seawater chemistry changes and marine carbon storage effectiveness are similar to previous studies. As expected, by the end of the injection period avoided emissions fall short of the targeted 70 Gt<mspace linebreak="nobreak" width="0.125em"/>C by 16–30 % as a result of carbon cycle feedbacks and backfluxes in both land and ocean reservoirs. The target emissions reduction in the parameter perturbation simulations is about 0.2 and 2 % more at the end of the injection period and about 9 % less to 1 % more at the end of the simulations when compared to the unperturbed injection runs. An unexpected feature is the effect of the model's internal variability of deep-water formation in the Southern Ocean, which, in some model runs, causes additional oceanic carbon uptake after injection termination relative to a control run without injection and ...