Decadal‐Scale Increases of Anthropogenic CO2 in Antarctic Bottom Water in the Indian and Western Pacific Sectors of the Southern Ocean

Murata, Akihiko; Kumamoto, Yuichiro; Sasaki, Ken‐ichi

doi:10.1029/2018gl080604

Cited by 9 publications

(23 citation statements)

References 44 publications

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“…Our data further indicate rapid anomalies in some periods suggesting that for decadal to long-term estimates care have to be taken when analyzing the change in Cant from data sets collected 10 or 20 years apart (e.g. Williams et al, 2015;Murata et al, 2019).…”

Section: Resultsmentioning

confidence: 76%

“…Cant have also been investigated in other SO regions, but limited to 2 to 4 reoccupations (Murata et al, 2019;Williams et al, 2015;Pardo et al, 2017). Given the Cant variability depicted at our location (Fig.…”

Section: Cant Trends and Variabilitymentioning

confidence: 93%

“…Nowadays, the distinction of water masses is usually performed according to neutral density (γ n ) layers. In the SO, CDW and AABW properties are generally well defined in the range 28.15-28.27 kg.m -3 and 28.27-bottom respectively (Orsi et al, 1999;Murata et al 2019). However, to interpret the long-term variability of the properties in the AABWs at our location, we prefer to adjust the AABW layer in a narrow band, and select the samples for γ n > 28.35 kg.m -3 (range starting at 4200m to 4600m depending on the year, see Fig.…”

Section: Aabw Definitionmentioning

confidence: 99%

“…4a), different trends can be deduced from limited reoccupations. As an example, Murata et al, (2019)…”

Section: Cant Trends and Variabilitymentioning

confidence: 99%

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Variability and stability of anthropogenic CO2 in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

Mahieu¹,

Monaco²,

Metzl³

et al. 2020

Preprint

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Abstract. Antarctic bottom waters (AABWs) are known as a long term sink for anthropogenic CO2 (Cant) but is hardly quantified because of the scarcity of the observations, specifically at an interannual scale. We present in this manuscript an original dataset combining 40 years of carbonate system observations in the Indian sector of the Southern Ocean (Enderby Basin) to evaluate and interpret the interannual variability of Cant in the AABW. This investigation is based on regular observations collected at the same location (63° E/56.5° S) in the frame of the French observatory OISO from 1998 to 2018 extended by GEOSECS and INDIGO observations (1978, 1985 and 1987). At this location the main sources of AABW sampled is the fresh and younger Cape Darnley bottom water (CDBW) and the Weddell Sea deep water (WSDW). Our calculations reveal that Cant concentrations increased significantly in AABW, from about + 7 µmol kg-1 in 1978–1987 to + 13 µmol kg-1 in 2010–2018. This is comparable to previous estimates in other SO basins, with the exception of bottom waters close to their formation sites where Cant concentrations are about twice as large. Our analysis shows that the CT and Cant increasing rates in AABW are about the same over the period 1978–2018, and we conclude that the long-term change in CT is mainly due to the uptake of anthropogenic CO2 in the different formation regions. This is however modulated by significant interannual to pluriannual variability associated with variations in hydrological (ϴ, S) and biogeochemical (CT, AT, O2) properties. A surprising result is the apparent stability of Cant concentrations in recent years despite the increase in CT and the gradual acceleration of atmospheric CO2. The Cant sequestration by AABWs is more variable than expected and depends on a complex combination of physical, chemical and biological processes at the formation sites and during the transit of the different AABWs. The interannual variability at play in AABW needs to be carefully considered on the extrapolated estimation of Cant sequestration based on sparse observations over several years.

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Section: Resultsmentioning

confidence: 76%

Section: Cant Trends and Variabilitymentioning

confidence: 93%

Section: Aabw Definitionmentioning

confidence: 99%

“…4a), different trends can be deduced from limited reoccupations. As an example, Murata et al, (2019)…”

Section: Cant Trends and Variabilitymentioning

confidence: 99%

See 2 more Smart Citations

Variability and stability of anthropogenic CO2 in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

Mahieu¹,

Monaco²,

Metzl³

et al. 2020

Preprint

View full text Add to dashboard Cite

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“…This is, however, not the case in polynyas, and several studies have reported significant C ant signals in AABW formation regions, likely due to the uptake of CO 2 induced by high primary production (Sandrini et al, 2007;van Heuven et al, 2011van Heuven et al, , 2014Shadwick et al, 2014;Roden et al, 2016). However, little is known about the variability and evolution of the CO 2 fluxes in AABW formation regions, and since biological and physical processes are strongly impacted by seasonal and interannual climatic variations (Fukamachi et al, 2000;Gordon et al, 2010;McKee et al, 2011;Gordon et al, 2015;Gruber et al, 2019b), the amount of C ant stored in the AABW may be very variable, which could bias the estimates of C ant trends derived from datasets collected several years apart (e.g., Williams et al, 2015;Pardo et al, 2017;Murata et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Variability and stability of anthropogenic CO2 in Antarctic Bottom Water observed in the Indian sector of the Southern Ocean, 1978–2018

et al. 2020

View full text Add to dashboard Cite

Abstract. Antarctic Bottom Water (AABW) is known as a long-term sink for anthropogenic CO2 (Cant), but the sink is hardly quantified because of the scarcity of observations, specifically at an interannual scale. We present in this paper an original dataset combining 40 years of carbonate system observations in the Indian sector of the Southern Ocean (Enderby Basin) to evaluate and interpret the interannual variability of Cant in the AABW. This investigation is based on regular observations collected at the same location (63∘ E–56.5∘ S) in the framework of the French observatory OISO from 1998 to 2018 extended by GEOSECS and INDIGO observations (1978, 1985 and 1987). At this location the main sources of AABW sampled is the low-salinity Cape Darnley Bottom Water (CDBW) and the Weddell Sea Deep Water (WSDW). Our calculations reveal that Cant concentrations increased significantly in the AABW, from an average concentration of 7 µmol kg−1 calculated for the period 1978–1987 to an average concentration of 13 µmol kg−1 for the period 2010–2018. This is comparable to previous estimates in other Southern Ocean (SO) basins, with the exception of bottom water close to formation sites where Cant concentrations are about twice as large. Our analysis shows that total carbon (CT) and Cant increasing rates in the AABW are about the same over the period 1978–2018, and we conclude that the long-term change in CT is mainly due to the uptake of Cant in the different formation regions. This is, however, modulated by significant interannual to multi-annual variability associated with variations in hydrographic (potential temperature, Θ; salinity, S) and biogeochemical (CT; total alkalinity, AT; dissolved oxygen, O2) properties. A surprising result is the apparent stability of Cant concentrations in recent years despite the increase in CT and the gradual acceleration of atmospheric CO2. The interannual variability at play in AABW needs to be carefully considered in the extrapolated estimation of Cant sequestration based on sparse observations over several years.

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Annually-resolved propagation of CFCs and SF6 in the global ocean over eight decades

Cimoli

Gebbie

Purkey

et al. 2022

Preprint

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Oceanic transient tracers, such as chlorofluorocarbons (CFCs) and sulfur-hexafluoride (SF6), trace the propagation of intermediateto-abyssal water masses in the ocean interior. Their temporal and spatial sparsity, however, has limited their utility in quantifying the global ocean circulation and its decadal variability. The Time-Correction Method presented here is a new approach to leverage the available CFCs and SF6 observations to solve for the Green's functions describing the steady-state transport from the surface to the ocean interior. From the Green's functions, we reconstruct global tracer concentrations (and associated uncertainties) in the ocean interior at annual resolution (1940 to 2021). The spatial resolution includes 50 neutral density levels that span the water column along WOCE/GO-SHIP lines. The reconstructed tracer concentrations return a global view of CFCs and SF6 spreading into new regions of the interior ocean, such as the deep north-western Pacific. For example, they capture the southward spreading and equatorial recirculation of distinct NADW components, and the spreading of CFC-rich AABW out of the Southern Ocean and into the North Pacific, East Indian, and West Atlantic. The reconstructed tracer concentrations fit the data in most locations (˜75%), indicating that a steady-state circulation holds for the most part. Discrepancies between the reconstructed and observed concentrations offer insight into ventilation rate changes on decadal timescales. As an example, we infer decadal changes in Subantartic Mode Water (SAMW) and find an increase in SAMW ventilation from 1992 to 2014, highlighting the skill of the time-correction method in leveraging the sparse tracer observations.

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Decadal‐Scale Increases of Anthropogenic CO₂ in Antarctic Bottom Water in the Indian and Western Pacific Sectors of the Southern Ocean

Cited by 9 publications

References 44 publications

Variability and stability of anthropogenic CO<sub>2</sub> in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

Variability and stability of anthropogenic CO<sub>2</sub> in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

Variability and stability of anthropogenic CO<sub>2</sub> in Antarctic Bottom Water observed in the Indian sector of the Southern Ocean, 1978–2018

Annually-resolved propagation of CFCs and SF6 in the global ocean over eight decades

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Decadal‐Scale Increases of Anthropogenic CO2 in Antarctic Bottom Water in the Indian and Western Pacific Sectors of the Southern Ocean

Cited by 9 publications

References 44 publications

Variability and stability of anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

Variability and stability of anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

Variability and stability of anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; in Antarctic Bottom Water observed in the Indian sector of the Southern Ocean, 1978–2018

Annually-resolved propagation of CFCs and SF6 in the global ocean over eight decades

Contact Info

Product

Resources

About

Decadal‐Scale Increases of Anthropogenic CO₂ in Antarctic Bottom Water in the Indian and Western Pacific Sectors of the Southern Ocean

Variability and stability of anthropogenic CO<sub>2</sub> in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

Variability and stability of anthropogenic CO<sub>2</sub> in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

Variability and stability of anthropogenic CO<sub>2</sub> in Antarctic Bottom Water observed in the Indian sector of the Southern Ocean, 1978–2018