A committed fourfold increase in ocean oxygen loss

Oschlies, Andreas

doi:10.1038/s41467-021-22584-4

Cited by 64 publications

(36 citation statements)

References 53 publications

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“…The two main driving mechanisms are the reduced solubility in the warming ocean and the decelerating overturning circulation. The longterm decline of oxygen is especially obvious at depth ( 1200m), which is induced by increasing deep water residence times and the accumulation of respiratory oxygen deficit under global warming (Oschlies et al, 2019;Oschlies, 2021).…”

Section: Impacts On Dissolved Oxygenmentioning

confidence: 99%

“…Notably, atmospheric CO 2 stops decreasing by year 2780 and rebounds afterwards even though MOS continues to sequester carbon. This can be explained by a recurrent deep convection in the Southern Ocean around year 2800 that accelerates oceanic carbon leakage back to the atmosphere (Martin et al, 2013;Reith et al, 2016;Oschlies, 2021). Meanwhile, the leakage of MOS-captured carbon eventually offsets the MOS carbon sequestration (Sect.4.6).…”

Section: Impacts On Dissolved Oxygenmentioning

confidence: 99%

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Carbon Dioxide Removal via Macroalgae Open-ocean Mariculture and Sinking: An Earth System Modeling Study

Keller

Oschlies

2022

Preprint

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Abstract. In this study we investigate open-ocean macroalgae mariculture and sinking (MOS) as ocean-based carbon dioxide removal (CDR) method. Embedding a macroalgae model into an Earth system model, we simulate macroalgae mariculture in the open-ocean surface layer followed by fast sinking of the carbon-rich macroalgal biomass to the deep seafloor (depth > 3,000 m). We also test the combination of MOS with artificial upwelling (AU), which fertilizes the macroalgae by pumping nutrient-rich deeper water to the surface. The simulations are done under RCP4.5 a moderate emission pathway. When deployed globally between years 2020 and 2100, the simulated CDR potential of MOS is 270 PgC, which is further boosted by AU to 447 PgC. More than half of MOS-sequestered carbon retains in the ocean after cessation at year 2100 until year 3000. The major side effect of MOS on pelagic ecosystems is the reduction of phytoplankton net primary production (PNPP) due to the nutrient competition and canopy shading by macroalgae. MOS shrinks the mid layer oxygen minimum zones (OMZs) by reducing the organic matter export to, and remineralization in, subsurface and intermediate waters, while it creates new OMZs on the seafloor by oxygen consumption from remineralization of sunken biomass. MOS also impacts the global carbon cycle, reduces the atmospheric and terrestrial carbon reservoir when enhancing the ocean carbon reservoir. MOS also enriches the dissolved inorganic carbon in the deep ocean. Effects are mostly reversible after cessation of MOS, though recovery is not complete by year 3000. In a sensitivity experiment without remineralization of sunk MOS biomass, the entire MOS-captured carbon is permanently stored in the ocean, but the lack of remineralized nutrients causes a long-term nutrient decline in the surface layers and thus reduces PNPP. Our results suggest that MOS has a considerable potential as an ocean-based CDR method. However, MOS has inherent side effects on marine ecosystems and biogeochemistry, which will require a careful evaluation beyond this first idealized modeling study.

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Section: Impacts On Dissolved Oxygenmentioning

confidence: 99%

Section: Impacts On Dissolved Oxygenmentioning

confidence: 99%

Carbon Dioxide Removal via Macroalgae Open-ocean Mariculture and Sinking: An Earth System Modeling Study

Keller

Oschlies

2022

Preprint

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“…The oxygen content in the inflowing water is decreased by 4% for each degree of warming applying the historic relationship between ocean warming and deoxygenation observed over the last decades (Schmidtko et al 2017). It should, however, be noted that ocean warming may induce even stronger oxygen losses on centennial to millennial time scales (Oschlies 2021). As outlined in the supplementary information, net primary production, autotrophic nitrogen fixation and PON degradation in the surface ocean increase with ocean warming (Eq.…”

Section: Response To Ocean Warmingmentioning

confidence: 88%

Biogeochemical feedbacks may amplify ongoing and future ocean deoxygenation: a case study from the Peruvian oxygen minimum zone

et al. 2022

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A new box model is employed to simulate the oxygen-dependent cycling of nutrients in the Peruvian oxygen minimum zone (OMZ). Model results and data for the present state of the OMZ indicate that dissolved iron is the limiting nutrient for primary production and is provided by the release of dissolved ferrous iron from shelf and slope sediments. Most of the removal of reactive nitrogen occurs by anaerobic oxidation of ammonium where ammonium is delivered by aerobic organic nitrogen degradation. Model experiments simulating the effects of ocean deoxygenation and warming show that the productivity of the Peruvian OMZ will increase due to the enhanced release of dissolved iron from shelf and slope sediments. A positive feedback loop rooted in the oxygen-dependent benthic iron release amplifies, both, the productivity rise and oxygen decline in ambient bottom waters. Hence, a 1% decline in oxygen supply reduces oxygen concentrations in sub-surface waters of the continental margin by 22%. The trend towards enhanced productivity and amplified deoxygenation will continue until further phytoplankton growth is limited by the loss of reactive nitrogen. Under nitrogen-limitation, the redox state of the OMZ is stabilized by negative feedbacks. A further increase in productivity and transition to sulfidic conditions is only possible if the rate of nitrogen fixation increases drastically under anoxic conditions. Such a transition would lead to a wide-spread accumulation of toxic sulfide with detrimental consequences for fishery yields in the Peruvian OMZ that currently provides a significant fraction of the global fish catch.

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“…In a recent model study on future deep ocean deoxygenation, Oschlies (2021) posited that his work "calls for more research efforts to explore the baseline of these systems before the unavoidable change will hit". The present study represents a first step towards quantifying the impact of LSW formation and export on the supply of oxygen to the open Atlantic Ocean.…”

Section: Discussionmentioning

confidence: 99%

Oxygen export to the deep ocean following Labrador Sea Water formation

Koelling

Atamanchuk

Karstensen

et al. 2021

Preprint

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Abstract. The Labrador Sea in the North Atlantic Ocean is one of the few regions globally where oxygen from the atmosphere can reach the deep ocean directly. This is the result of wintertime convection, which homogenizes the water column to a depth of up to 2000 m, and brings deep water undersaturated in oxygen into contact with the atmosphere. In this study, we analyze how the intense oxygen uptake during Labrador Sea Water (LSW) formation affects the properties of the outflowing deep western boundary current, which ultimately feeds the upper part of the North Atlantic Deep Water layer in much of the Atlantic Ocean. Seasonal cycles of oxygen concentration, temperature, and salinity from a two-year time series collected by sensors moored at 600 m nominal depth in the outflowing boundary current at 53° N show that LSW is primarily exported in the months following the onset of convection, from March to August. During the rest of the year, properties of the outflow resemble those of Irminger Water, which enters the basin with the boundary current from the Irminger Sea. The input of newly ventilated LSW increases the oxygen concentration from 298 μmol L−1 in January to a maximum of 306 μmol L−1 in April. As a result of this LSW input, 1.57 × 1012 mol year−1 of oxygen are added to the outflowing boundary current, mostly during summer, equivalent to 49 % of the wintertime uptake from the atmosphere in the interior of the basin. The export of oxygen from the subpolar gyre associated with this direct southward pathway of LSW is estimated to supply about 71 % of the oxygen consumed annually in the upper North Atlantic Deep Water layer in the Atlantic Ocean between the equator and 50° N. Our results show that the formation of LSW is important for replenishing oxygen to the deep oceans, meaning that possible changes in its formation rate and ventilation due to climate change could have wide-reaching impacts on marine life.

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A committed fourfold increase in ocean oxygen loss

Cited by 64 publications

References 53 publications

Carbon Dioxide Removal via Macroalgae Open-ocean Mariculture and Sinking: An Earth System Modeling Study

Carbon Dioxide Removal via Macroalgae Open-ocean Mariculture and Sinking: An Earth System Modeling Study

Biogeochemical feedbacks may amplify ongoing and future ocean deoxygenation: a case study from the Peruvian oxygen minimum zone

Oxygen export to the deep ocean following Labrador Sea Water formation

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