Observed amplification of the seasonal CO2 cycle at the Southern Ocean Time Series

Shadwick, Elizabeth H.; Wynn-Edwards, Cathryn A.; Matear, Richard J.; Jansen, Peter; Schulz, Eric; Sutton, Adrienne J.

doi:10.3389/fmars.2023.1281854

Cited by 3 publications

(2 citation statements)

References 87 publications

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“…In the SAZ sector, the E MLP is responsible for about 23% of the annual total flux, which is in the range of estimates from the North Atlantic (5%-25%; Bol et al, 2018) and in good agreement with the high latitude mean (23%; Dall'Olmo et al, 2016). The SAZ sector is characterized by steady biological activity and very deep autumn (and winter) mixing (Shadwick et al, 2015(Shadwick et al, , 2023. The seasonality is dominated by an onset of productivity in early spring, followed by moderate but continuous productivity well into the autumn season (Shadwick et al, 2015;Weeding & Trull, 2014).…”

Section: Contributions To Carbon Export In the Subantarctic Regionmentioning

confidence: 62%

Carbon Export in the Subantarctic Zone Revealed by Multi‐Year Observations From Biogeochemical‐Argo Floats and Sediment Traps

Yang,

Wynn‐Edwards,

Strutton

et al. 2024

Global Biogeochemical Cycles

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The biological gravitational pump (BGP) and particle injection pumps (PIPs) are significant export pathways for particulate organic carbon from the surface ocean to the interior. Part of this exported carbon fuels remineralization in the mesopelagic ocean and part is sequestered in the deep ocean. Using observations from Biogeochemical‐Argo, we characterized the seasonality and magnitude of the BGP and two PIPs: the mixed layer pump (MLP) and eddy subduction pump (ESP), in the Australian sector of the Subantarctic Zone (SAZ sector). For the first time, float‐based estimates were rigorously combined with sediment trap flux (F1000) observations from the Southern Ocean Time Series (SOTS), to investigate these pumps' relative and cumulative contributions to carbon export. The BGP exports about 28.6 g C m−2 year−1, mostly during the productive season and dominates the F1000 seasonality. The MLP exports about 7.6 g C m−2 year−1, mostly while the mixing layer seasonally shoals; the ESP sporadically exports up to 100 mg C m−2 day−1, such that these two PIPs have a short but intense impact on the F1000. The carbon transfer efficiency is 3.6% in the SOTS region. An oxygen‐based annual net community production estimate (∼50 g C m−2 year−1) further strengthens this study, and suggests the BGP and MLP make the dominant contribution to the mesopelagic carbon budget. This is representative of the broader SAZ sector in terms of the magnitude and seasonality of carbon export, the consumption of organic material in the mesopelagic, and the organic carbon sequestration in the deep sea.

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Section: Contributions To Carbon Export In the Subantarctic Regionmentioning

confidence: 62%

Carbon Export in the Subantarctic Zone Revealed by Multi‐Year Observations From Biogeochemical‐Argo Floats and Sediment Traps

Yang,

Wynn‐Edwards,

Strutton

et al. 2024

Global Biogeochemical Cycles

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“…The SOTS observatory consists of two deep-water moorings, the Southern Ocean Flux Station (SOFS) and the SAZ sediment trap mooring. The SOFS mooring was first deployed in November 2011, with annual turn around and provides high temporal resolution air-sea CO 2 observations in subantarctic waters (Shadwick et al, 2023). Water temperature, salinity, wind speed and chlorophyll fluorescence are measured by instruments on the surface buoy.…”

Section: Southern Ocean Time Series Observationsmentioning

confidence: 99%

Drivers of Air‐Sea CO₂ Flux in the Subantarctic Zone Revealed by Time Series Observations

Yang,

Wynn‐Edwards,

Strutton

et al. 2024

Global Biogeochemical Cycles

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The subantarctic zone is an important region in the Southern Ocean with respect to its influence on air‐sea CO2 exchange and the global ocean carbon cycle. However, understanding of the magnitude and drivers of the flux are still being refined. Using observations from the Southern Ocean Time Series (SOTS) station (∼47°S, 142°E) and auxiliary data, we developed a multiple linear regression model to compute the sea surface partial pressure of CO2 (pCO2) over the past two decades. The mean amplitude of the pCO2 seasonal cycle between 2004 and 2021 was 44 μatm (range 30–54 μatm). Summer minima ranged from 310 to 370 μatm and winter maxima were near equilibrium with the atmosphere. The non‐thermal (i.e., biological processes and mixing) contribution to the seasonal variability in pCO2 was several times larger than the thermal contribution. The SOTS region acted as a net carbon sink at annual time scales, with mean magnitude of 6.0 mmol m−2 d−1. The positive phase of the Southern Annular Mode (SAM) increased ocean carbon uptake primarily through an increase in wind speed at zero time lag. Increased surface pCO2 was correlated with a positive SAM with a lag of 4 months, mainly due to reduced biological uptake and increased mixing. During the autotrophic season, pCO2 was predominantly impacted by primary productivity, whereas water mass movement, inferred by temperature and salinity anomalies, had a larger impact on the heterotrophic season. In general, mesoscale processes such as eddies and frontal movement impact the local biogeochemical features more than the SAM.

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Anthropogenic CO₂, air–sea CO₂ fluxes, and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51° S–68° E)

Metzl,

Lo Monaco,

Leseurre

et al. 2024

Ocean Sci.

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Abstract. The temporal variation of the carbonate system, air–sea CO2 fluxes, and pH is analyzed in the southern Indian Ocean, south of the polar front, based on in situ data obtained from 1985 to 2021 at a fixed station (50°40′ S–68°25′ E) and results from a neural network model that reconstructs the fugacity of CO2 (fCO2) and fluxes at monthly scale. Anthropogenic CO2 (Cant) is estimated in the water column and is detected down to the bottom (1600 m) in 1985, resulting in an aragonite saturation horizon at 600 m that migrated up to 400 m in 2021 due to the accumulation of Cant. At the subsurface, the trend of Cant is estimated at +0.53±0.01 µmol kg−1 yr−1 with a detectable increase in the trend in recent years. At the surface during austral winter the oceanic fCO2 increased at a rate close to or slightly lower than in the atmosphere. To the contrary, in summer, we observed contrasting fCO2 and dissolved inorganic carbon (CT) trends depending on the decade and emphasizing the role of biological drivers on air–sea CO2 fluxes and pH inter-annual variability. The regional air–sea CO2 fluxes evolved from an annual source to the atmosphere of 0.8 molC m−2 yr−1 in 1985 to a sink of −0.5 molC m−2 yr−1 in 2020. Over 1985–2020, the annual pH trend in surface waters of -0.0165±0.0040 per decade was mainly controlled by the accumulation of anthropogenic CO2, but the summer pH trends were modulated by natural processes that reduced the acidification rate in the last decade. Using historical data from November 1962, we estimated the long-term trend for fCO2, CT, and pH, confirming that the progressive acidification was driven by the atmospheric CO2 increase. In 59 years this led to a diminution of 11 % for both aragonite and calcite saturation state. As atmospheric CO2 is expected to increase in the future, the pH and carbonate saturation state will decrease at a faster rate than observed in recent years. A projection of future CT concentrations for a high emission scenario (SSP5-8.5) indicates that the surface pH in 2100 would decrease to 7.32 in winter. This is up to −0.86 lower than pre-industrial pH and −0.71 lower than pH observed in 2020. The aragonite undersaturation in surface waters would be reached as soon as 2050 (scenario SSP5-8.5) and 20 years later for a stabilization scenario (SSP2-4.5) with potential impacts on phytoplankton species and higher trophic levels in the rich ecosystems of the Kerguelen Islands area.

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Observed amplification of the seasonal CO2 cycle at the Southern Ocean Time Series

Cited by 3 publications

References 87 publications

Carbon Export in the Subantarctic Zone Revealed by Multi‐Year Observations From Biogeochemical‐Argo Floats and Sediment Traps

Carbon Export in the Subantarctic Zone Revealed by Multi‐Year Observations From Biogeochemical‐Argo Floats and Sediment Traps

Drivers of Air‐Sea CO₂ Flux in the Subantarctic Zone Revealed by Time Series Observations

Anthropogenic CO₂, air–sea CO₂ fluxes, and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51° S–68° E)

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Observed amplification of the seasonal CO2 cycle at the Southern Ocean Time Series

Cited by 3 publications

References 87 publications

Carbon Export in the Subantarctic Zone Revealed by Multi‐Year Observations From Biogeochemical‐Argo Floats and Sediment Traps

Carbon Export in the Subantarctic Zone Revealed by Multi‐Year Observations From Biogeochemical‐Argo Floats and Sediment Traps

Drivers of Air‐Sea CO2 Flux in the Subantarctic Zone Revealed by Time Series Observations

Anthropogenic CO2, air–sea CO2 fluxes, and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51° S–68° E)

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Product

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Drivers of Air‐Sea CO₂ Flux in the Subantarctic Zone Revealed by Time Series Observations

Anthropogenic CO₂, air–sea CO₂ fluxes, and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51° S–68° E)