Variability of North Atlantic CO 2 fluxes for the 2000–2017 period estimated from atmospheric inverse analyses

Chen, Zhaohui; Suntharalingam, Parvadha; Watson, Andrew J.; Schuster, Ute; Zhu, Jiang; Zeng, Ning

We present new estimates of the regional North Atlantic (15–80inline-formula N) COinline-formula2 flux for the 2000–2017 period using atmospheric COinline-formula2 measurements from the NOAA long-term surface site network in combination with an atmospheric carbon cycle data assimilation system (GEOS-Chem–LETKF, Local Ensemble Transform Kalman Filter). We assess the sensitivity of flux estimates to alternative ocean COinline-formula2 prior flux distributions and to the specification of uncertainties associated with ocean fluxes. We present a new scheme to characterize uncertainty in ocean prior fluxes, derived from a set of eight surface inline-formulapCOinline-formula2-based ocean flux products, and which reflects uncertainties associated with measurement density and inline-formulapCOinline-formula2-interpolation methods. This scheme provides improved model performance in comparison to fixed prior uncertainty schemes, based on metrics of model–observation differences at the network of surface sites. Long-term average posterior flux estimates for the 2000–2017 period from our GEOS-Chem–LETKF analyses are inline-formula−0.255 inline-formula± 0.037 PgC yrinline-formula−1 for the subtropical basin (15–50inline-formula N) and inline-formula−0.203 inline-formula± 0.037 PgC yrinline-formula−1 for the subpolar region (50–80inline-formula N, eastern boundary at 20inline-formula E). Our basin-scale estimates of interannual variability (IAV) are 0.036 inline-formula± 0.006 and 0.034 inline-formula± 0.009 PgC yrinline-formula−1 for subtropical and subpolar regions, respectively. We find statistically significant trends in carbon uptake for the subtropical and subpolar North Atlantic of inline-formula−0.064 inline-formula± 0.007 and inline-formula−0.063 inline-formula± 0.008 PgC yrinline-formula−1 decadeinline-formula−1; these trends are of comparable magnitude to estimates from surface ocean inline-formulapCOinline-formula2-based flux products, but they are larger, by a factor of 3–4, than trends estimated from global ocean biogeochemistry models.

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Chen, Zhaohui / Suntharalingam, Parvadha / Watson, Andrew J. / et al: Variability of North Atlantic CO2 fluxes for the 2000–2017 period estimated from atmospheric inverse analyses. 2021. Copernicus Publications.

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