How much has the road to climate solutions just narrowed?
For years, Oschlies et al have been helping the rest of us see the enormous lungs of the deep. Back in 2021, Oschlies and co-authors showed that carbon emissions already gushed into the atmosphere will ultimately drive another 4x more oxygen depletion in the ocean. In a new paper, Oschlies and co-authors just showed that efforts to accelerate the ocean's biological powers for carbon cleanup could exact a steep price, paid in oxygen. How much does this narrow our options for mopping up the carbon mess?
Excerpt:
Global warming is a main cause for current ocean deoxygenation. A deployment of marine carbon dioxide removal (CDR) for mitigating global warming could therefore also be viewed as a measure for mitigating ocean deoxygenation if, and only if, the respective CDR measure itself does not lead to a larger oxygen loss than the reduction in atmospheric CO2 would prevent. We here review the current state of knowledge regarding the potential impacts of various marine CDR (mCDR) options onto ocean oxygen, a key ocean state variable and an essential element for all higher forms of marine life. Using results from global model simulations, we show that biotic approaches, such as ocean fertilization, macroalgae cultivation and sinking, and placement of organic matter that is prone to remineralization, can lead to a loss in seawater dissolved oxygen that is 4–40 times larger than the oxygen gain that would result from the CDR-induced reduction in global warming only.
Source: Potential impacts of marine carbon dioxide removal on ocean oxygen
Andreas Oschlies et al 2025 Environ. Res. Lett. 20 073002
DOI 10.1088/1748-9326/ade0d4
Schematic of the different marine carbon dioxide removal (mCDR) methods discussed in this study. Pink shading indicates possible reduction in dissolved oxygen resulting from the respective open-ocean biotic mCDR activity via enhanced respiration in the water column, green shading for iron fertilization and artificial upwelling indicates fertilization-induced enhanced photosynthesis in the surface waters. Inserts indicate the mCDR-induced additional O2 production (green) and O2 consumption (white). For Blue carbon, the dashed line refers to the baseline and the solid line to the enhanced diel cycle due to Blue carbon deployment.
