TY - JOUR
T1 - Reassessing Southern Ocean Air-Sea CO2 Flux Estimates With the Addition of Biogeochemical Float Observations
AU - Bushinsky, Seth M.
AU - Landschützer, Peter
AU - Rödenbeck, Christian
AU - Gray, Alison R.
AU - Baker, David
AU - Mazloff, Matthew R.
AU - Resplandy, Laure
AU - Johnson, Kenneth S.
AU - Sarmiento, Jorge L.
N1 - Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.
PY - 2019/11/1
Y1 - 2019/11/1
N2 - New estimates of pCO2 from profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project have demonstrated the importance of wintertime outgassing south of the Polar Front, challenging the accepted magnitude of Southern Ocean carbon uptake (Gray et al., 2018, https://doi:10.1029/2018GL078013). Here, we put 3.5 years of SOCCOM observations into broader context with the global surface carbon dioxide database (Surface Ocean CO2 Atlas, SOCAT) by using the two interpolation methods currently used to assess the ocean models in the Global Carbon Budget (Le Quéré et al., 2018, https://doi:10.5194/essd-10-2141-2018) to create a ship-only, a float-weighted, and a combined estimate of Southern Ocean carbon fluxes (<35°S). In our ship-only estimate, we calculate a mean uptake of −1.14 ± 0.19 Pg C/yr for 2015–2017, consistent with prior studies. The float-weighted estimate yields a significantly lower Southern Ocean uptake of −0.35 ± 0.19 Pg C/yr. Subsampling of high-resolution ocean biogeochemical process models indicates that some of the differences between float and ship-only estimates of the Southern Ocean carbon flux can be explained by spatial and temporal sampling differences. The combined ship and float estimate minimizes the root-mean-square pCO2 difference between the mapped product and both data sets, giving a new Southern Ocean uptake of −0.75 ± 0.22 Pg C/yr, though with uncertainties that overlap the ship-only estimate. An atmospheric inversion reveals that a shift of this magnitude in the contemporary Southern Ocean carbon flux must be compensated for by ocean or land sinks within the Southern Hemisphere.
AB - New estimates of pCO2 from profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project have demonstrated the importance of wintertime outgassing south of the Polar Front, challenging the accepted magnitude of Southern Ocean carbon uptake (Gray et al., 2018, https://doi:10.1029/2018GL078013). Here, we put 3.5 years of SOCCOM observations into broader context with the global surface carbon dioxide database (Surface Ocean CO2 Atlas, SOCAT) by using the two interpolation methods currently used to assess the ocean models in the Global Carbon Budget (Le Quéré et al., 2018, https://doi:10.5194/essd-10-2141-2018) to create a ship-only, a float-weighted, and a combined estimate of Southern Ocean carbon fluxes (<35°S). In our ship-only estimate, we calculate a mean uptake of −1.14 ± 0.19 Pg C/yr for 2015–2017, consistent with prior studies. The float-weighted estimate yields a significantly lower Southern Ocean uptake of −0.35 ± 0.19 Pg C/yr. Subsampling of high-resolution ocean biogeochemical process models indicates that some of the differences between float and ship-only estimates of the Southern Ocean carbon flux can be explained by spatial and temporal sampling differences. The combined ship and float estimate minimizes the root-mean-square pCO2 difference between the mapped product and both data sets, giving a new Southern Ocean uptake of −0.75 ± 0.22 Pg C/yr, though with uncertainties that overlap the ship-only estimate. An atmospheric inversion reveals that a shift of this magnitude in the contemporary Southern Ocean carbon flux must be compensated for by ocean or land sinks within the Southern Hemisphere.
KW - SOCCOM
KW - Southern Ocean
KW - biogeochemical profiling floats
KW - global carbon cycle
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U2 - 10.1029/2019GB006176
DO - 10.1029/2019GB006176
M3 - Article
C2 - 32025087
AN - SCOPUS:85075477826
SN - 0886-6236
VL - 33
SP - 1370
EP - 1388
JO - Global Biogeochemical Cycles
JF - Global Biogeochemical Cycles
IS - 11
ER -