Strong Southern Ocean carbon uptake evident in airborne observations

Long, Matthew C.; Stephens, B. B.; McKain, Kathryn; Sweeney, Colm; Keeling, Ralph F.; Kort, E. A.; Morgan, Eric J.; Bent, J. D.; Chandra, Naveen; Chevallier, F.; Commane, R.; Daube, Bruce C.; Krummel, Paul B.; Loh, Zoë; Luijkx, Ingrid T.; Munro, David R.; Patra, Prabir K.; Peters, Wouter; Ramonet, Michel; Rödenbeck, Christian; Stavert, Ann R.; Tans, Pieter P.; Wofsy, Steven C.

doi:10.1126/science.abi4355

Cited by 51 publications

(42 citation statements)

References 72 publications

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“…A considerable rate of CO 2 uptake is also observed in the Southern Ocean region; the CO 2 flux increased from −0.12 ± 0.07 PgC yr −1 in 2001-2009 to −0.33 ± 0.06 PgC yr −1 in 2010-2019. The Southern Ocean CO 2 flux for 2010-2019 agrees well with a recent assessment of −0.53 ± 0.23 PgC yr −1 (net uptake) in the region south of 45 • S during 2009-2018 (Long et al, 2021).…”

Section: Regional Co 2 Fluxes and Flux Uncertaintiessupporting

confidence: 87%

Estimated regional CO₂flux and uncertainty based on an ensemble of atmospheric CO₂inversions

et al. 2022

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Abstract. Global and regional sources and sinks of carbon across the earth's surface have been studied extensively using atmospheric carbon dioxide (CO2) observations and atmospheric chemistry-transport model (ACTM) simulations (top-down/inversion method). However, the uncertainties in the regional flux distributions remain unconstrained due to the lack of high-quality measurements, uncertainties in model simulations, and representation of data and flux errors in the inversion systems. Here, we assess the representation of data and flux errors using a suite of 16 inversion cases derived from a single transport model (MIROC4-ACTM) but different sets of a priori (bottom-up) terrestrial biosphere and oceanic fluxes, as well as prior flux and observational data uncertainties (50 sites) to estimate CO2 fluxes for 84 regions over the period 2000–2020. The inversion ensembles provide a mean flux field that is consistent with the global CO2 growth rate, land and ocean sink partitioning of −2.9 ± 0.3 (± 1σ uncertainty on the ensemble mean) and −1.6 ± 0.2 PgC yr−1, respectively, for the period 2011–2020 (without riverine export correction), offsetting about 22 %–33 % and 16 %–18 % of global fossil fuel CO2 emissions. The rivers carry about 0.6 PgC yr−1 of land sink into the deep ocean, and thus the effective land and ocean partitioning is −2.3 ± 0.3 and −2.2 ± 0.3, respectively. Aggregated fluxes for 15 land regions compare reasonably well with the best estimations for the 2000s (∼ 2000–2009), given by the REgional Carbon Cycle Assessment and Processes (RECCAP), and all regions appeared as a carbon sink over 2011–2020. Interannual variability and seasonal cycle in CO2 fluxes are more consistently derived for two distinct prior fluxes when a greater degree of freedom (increased prior flux uncertainty) is given to the inversion system. We have further evaluated the inversion fluxes using meridional CO2 distributions from independent (not used in the inversions) aircraft and surface measurements, suggesting that the ensemble mean flux (model–observation mean ± 1σ standard deviation = −0.3 ± 3 ppm) is best suited for global and regional CO2 flux budgets than an individual inversion (model–observation 1σ standard deviation = −0.35 ± 3.3 ppm). Using the ensemble mean fluxes and uncertainties for 15 land and 11 ocean regions at 5-year intervals, we show promise in the capability to track flux changes toward supporting the ongoing and future CO2 emission mitigation policies.

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Section: Regional Co 2 Fluxes and Flux Uncertaintiessupporting

confidence: 87%

Estimated regional CO₂flux and uncertainty based on an ensemble of atmospheric CO₂inversions

et al. 2022

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“…Thus, assessments based on the seasonal change in surface DIC stocks (this work), or annual mean air‐sea CO 2 fluxes (Bushinsky et al., 2019; Gray et al., 2018) could indicate a recent change in the ocean air‐sea carbon flux in the Antarctic‐Southern Zone. Alternative explanations involving bias in pCO 2 estimates (Long et al., 2021) or sampling (Bushinsky et al., 2019) could also account for the difference in flux, but these explanations would not account for the apparent change in ΔDIC/ΔNO 3 we compute at 55°S relative to the value derived from the Takahashi climatology. Observed ocean and atmospheric changes such as deepening mixed layers (Sallée et al., 2021), warming (Gille, 2008; Roemmich et al., 2015), freshening (Swart et al., 2018), increasing currents (Shi et al., 2021), and strengthening winds (Swart and Fyfe, 2012; Toggweiler and Russell, 2008) may be associated with a shift in CO 2 gas flux.…”

Section: Discussionmentioning

confidence: 91%

“…The change in flux reported by Gray et al (2018), relative to the ship-based products in the Antarctic-Southern Zone, is of the correct magnitude and direction to account for the difference of ΔDIC/ΔNO 3 in the float and Takahashi data sets. However, there are also suggestions of a systematic bias in the float data (Long et al, 2021). A relatively small, systematic offset (∼0.005) in the quality controlled float pH data used to compute pCO 2 and CO 2 flux could account for much of the difference in the Antarctic-Southern Zone.…”

Section: Implications Of δDic/δno 3 For J Co2mentioning

confidence: 99%

Carbon to Nitrogen Uptake Ratios Observed Across the Southern Ocean by the SOCCOM Profiling Float Array

et al. 2022

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Measurements of pH and nitrate from the Southern Ocean Carbon and Climate Observations and Modeling array of profiling floats were used to assess the ratios of dissolved inorganic carbon (DIC) and nitrate (NO3) uptake during the spring to summer bloom period throughout the Southern Ocean. Two hundred and forty‐three bloom periods were observed by 115 floats from 30°S to 70°S. Similar calculations were made using the Takahashi surface DIC and nitrate climatology. To separate the effects of atmospheric CO2 exchange and mixing from phytoplankton uptake, the ratios of changes in DIC to nitrate of surface waters (ΔDIC/ΔNO3) were computed in the Biogeochemical Southern Ocean State Estimate (B‐SOSE) model. Phytoplankton uptake of DIC and nitrate are fixed in B‐SOSE at the Redfield Ratio (RR; 6.6 mol C/mol N). Deviations in the B‐SOSE ΔDIC/ΔNO3 must be due to non‐biological effects of CO2 gas exchange and mixing. ΔDIC/ΔNO3 values observed by floats and in the Takahashi climatology were corrected for the non‐biological effects using B‐SOSE. The corrected, in situ biological uptake ratio (C:N) occurs at values similar to the RR, with two major exceptions. North of 40°S biological DIC uptake is observed with little or no change in nitrate giving high C:N. In the latitude band at 55°S, the Takahashi data give a low C:N value, while floats are high. This may be due to a change in CO2 air‐sea exchange in this region from uptake during the Takahashi reference year of 2005 to outgassing of CO2 during the years sampled by floats.

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“…Floats can augment shipboard data, in particular because of superior wintertime coverage. As carbon uptake in the Southern Ocean has strong seasonal signature 7,8,56 , in part due to biological activity, shipboard measurements, which are predominantly taken in the summer, may be affected by small scale processes that drive local primary production rates to be spatially and temporally variable. Furthermore, it has been found that models using only data from floats produce Southern Ocean carbon uptake values that are onethird of those from models using only using shipboard data 22 .…”

Section: Discussionmentioning

confidence: 99%

“…Consequently, it is estimated that the Southern Ocean is responsible for approximately 40% of the oceanic carbon sink of the anthropogenic emissions 5 , where persistent zonal winds are strong and temperatures are relatively cold. Biological uptake of carbon has also been shown to play an important role in the Southern Ocean [6][7][8] . Biological uptake predominantly occurs in the spring and summer, importantly when CO 2 solubility is weak, and previous studies 6 have found decadal variability in primary production, which subsequently affects the ocean carbon sink.…”

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confidence: 99%

A deep-learning estimate of the decadal trends in the Southern Ocean carbon storage

Zemskova

Wan

et al. 2022

Nat Commun

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Uptake of atmospheric carbon by the ocean, especially at high latitudes, plays an important role in offsetting anthropogenic emissions. At the surface of the Southern Ocean south of 30∘S, the ocean carbon uptake, which had been weakening in 1990s, strengthened in the 2000s. However, sparseness of in-situ measurements in the ocean interior make it difficult to compute changes in carbon storage below the surface. Here we develop a machine-learning model, which can estimate concentrations of dissolved inorganic carbon (DIC) in the Southern Ocean up to 4 km depth only using data available at the ocean surface. Our model is fast and computationally inexpensive. We apply it to calculate trends in DIC concentrations over the past three decades and find that DIC decreased in the 1990s and 2000s, but has increased, in particular in the upper ocean since the 2010s. However, the particular circulation dynamics that drove these changes may have differed across zonal sectors of the Southern Ocean. While the near-surface decrease in DIC concentrations would enhance atmospheric CO2 uptake continuing the previously-found trends, weakened connectivity between surface and deep layers and build-up of DIC in deep waters could reduce the ocean’s carbon storage potential.

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Strong Southern Ocean carbon uptake evident in airborne observations

Cited by 51 publications

References 72 publications

Estimated regional CO₂flux and uncertainty based on an ensemble of atmospheric CO₂inversions

Estimated regional CO₂flux and uncertainty based on an ensemble of atmospheric CO₂inversions

Carbon to Nitrogen Uptake Ratios Observed Across the Southern Ocean by the SOCCOM Profiling Float Array

A deep-learning estimate of the decadal trends in the Southern Ocean carbon storage

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Strong Southern Ocean carbon uptake evident in airborne observations

Cited by 51 publications

References 72 publications

Estimated regional CO2flux and uncertainty based on an ensemble of atmospheric CO2inversions

Estimated regional CO2flux and uncertainty based on an ensemble of atmospheric CO2inversions

Carbon to Nitrogen Uptake Ratios Observed Across the Southern Ocean by the SOCCOM Profiling Float Array

A deep-learning estimate of the decadal trends in the Southern Ocean carbon storage

Contact Info

Product

Resources

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Estimated regional CO₂flux and uncertainty based on an ensemble of atmospheric CO₂inversions

Estimated regional CO₂flux and uncertainty based on an ensemble of atmospheric CO₂inversions