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Winter Air‐Sea CO 2 Fluxes Constructed From Summer Observations of the Polar Southern Ocean Suggest Weak Outgassing
Author(s) -
Mackay Neill,
Watson Andrew
Publication year - 2021
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2020jc016600
Subject(s) - outgassing , polar front , polar , sink (geography) , climatology , flux (metallurgy) , environmental science , oceanography , atmospheric sciences , geology , geography , chemistry , physics , materials science , cartography , organic chemistry , astronomy , metallurgy
The Southern Ocean plays an important role in the global oceanic uptake of CO 2 . Estimates of the air‐sea CO 2 flux are made using the partial pressure of CO 2 at the sea surface (p C O 2surf ), but winter observations of the region historically have been sparse, with almost no coverage in the Pacific or Indian ocean sectors south of the Polar front in the period 2004–2017. Here, we use summertime observations of relevant properties in this region to identify subsurface waters that were last in contact with the atmosphere in the preceding winter, and then reconstruct “pseudo observations” of the wintertimep C O 2surf . These greatly improve wintertime coverage south of the Polar Front in all sectors, improving the robustness of flux estimates there. We add the pseudo observations to other available observations ofp C O 2surfand use a multiple linear regression to produce a gap‐filled time‐evolving estimate ofp C O 2surffrom which we calculate the air‐sea flux. The inclusion of the pseudo observations increases outgassing at the beginning of the period, but the effect reduces with time. We estimate a 2004–2017 long‐term mean flux of −0.02 ± 0.02 Pg C yr −1 for the Southern Ocean south of the Polar Front, similar to comparable studies based on shipboardp C O 2surfdata. However, we diverge somewhat from an estimate which utilized autonomous float data for recent years: we find a small sink in 2017 of −0.08 ± 0.03 Pg C yr −1 where the float‐based estimate suggested a small source.