Geographical variations in the effectiveness and side effects of deep ocean carbon sequestration

Abstract

The capture and injection of carbon dioxide (CO2) into the deep ocean could provide a relatively long‐term mitigation of climate change, but would come at the expense of enhancing acidification at the seafloor. We employ an Earth system model to survey the regional differences in the effectiveness and side effects of CO2 injection. Sequestration efficiency, as calculated relative to the ‘natural’ invasion from the atmosphere that would occur in the absence of mitigation, is highest for injection in the deep NW Pacific, but can be negative for shallow sites. For higher climate sensitivities and greater total emissions, sequestration efficiency is enhanced, decreasing the relative cost and increasing its potential value as a form of mitigation. However, CO2 injection increases the total area of seafloor bathed in under‐saturated waters, with Atlantic sites inducing particularly large increases in seafloor undersaturation as well as having less favorable sequestration efficiency.

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

“…By comparing the With Emissions and Complete Mitigation simulations at all depths, we can determine how climate change affects FR. As in previous studies, our results show that FR is enhanced by climate change (Jain and Cao, 2005;Ridgwell et al, 2011). In the With Emissions simulations, values of FR are always higher than in the Complete Mitigation runs (Table 2).…”

“…Following previous studies (e.g., Jain and Cao, 2005;Ridgwell et al, 2011) Figure 1. Absolute changes in oceanic and land carbon between I-3000 and the RCP 8.5 control run (I-3000 simulation minus RCP 8.5 control run) at the end of the injection period (year 2120).…”

“…3.4.2), we cannot easily compare the Direct Air Capture run to the With Emissions simulations after the injection period. While ocean feedbacks in response to CO 2 injection and reduced atmospheric CO 2 levels have been discussed extensively in previous studies (e.g., Orr, 2004;IPCC, 2005;Ridgwell et al, 2011), we here additionally consider land feedbacks with the purpose of accounting for the entire Earth system's response to potential marine CO 2 injections.…”

“…These risks may be especially high for deep-sea benthic environments such as cold-water corals and sponge communities, which are adapted to special living conditions and thus may have a low capacity to acclimatize to rapid pH changes in their environment (e.g., IPCC, 2005;Schubert et al, 2006;Gehlen et al, 2014). In previous studies, relatively simple box model (e.g., Hoffert et al, 1979) and first-generation global ocean circulation models (Orr, 2004) were employed, focusing on the residence time of the injected CO 2 (i.e., effectiveness), as well as on changes in ocean chemistry (e.g., Orr et al, 2001;Orr, 2004;Jain and Cao, 2005;IPCC, 2005;Ridgwell et al, 2011).…”

Assessing the potential of calcium-based artificial ocean alkalinization to mitigate rising atmospheric CO2and ocean acidification

“…An increase in TA would also alter seawater constituents so that its acidity decreases. Thus, in contrast to direct sequestration of carbon into the deep ocean [ Ridgwell et al ., ] alkalinity enhancement, along with a drawdown of atmospheric CO 2 , would also drive ocean pH and the saturation state of CaCO 3 (referred to as Ω) to higher values thereby counteracting ongoing ocean acidification. Unmitigated, ocean acidification is likely to have diverse negative impacts on marine biodiversity, food webs, and ecosystems including decrease in calcification rates or changes in reproduction and physiology observed in some marine organisms [ Gattuso and Hansson , ].…”