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

• Published in: Biogeosciences
• Main Authors: Z. Chen, P. Suntharalingam, A. J. Watson, U. Schuster, J. Zhu, N. Zeng
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; North Atlantic
• Online Access: https://doi.org/10.5194/bg-18-4549-2021; https://doaj.org/article/02a873e5f0ee48cf944bb426a15a8a38

We present new estimates of the regional North Atlantic (15–80 ∘ N) CO 2 flux for the 2000–2017 period using atmospheric CO 2 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 CO 2 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 p CO 2 -based ocean flux products, and which reflects uncertainties associated with measurement density and p CO 2 -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 − 0.255 ± 0.037 PgC yr −1 for the subtropical basin (15–50 ∘ N) and − 0.203 ± 0.037 PgC yr −1 for the subpolar region (50–80 ∘ N, eastern boundary at 20 ∘ E). Our basin-scale estimates of interannual variability (IAV) are 0.036 ± 0.006 and 0.034 ± 0.009 PgC yr −1 for subtropical and subpolar regions, respectively. We find statistically significant trends in carbon uptake for the subtropical and subpolar North Atlantic of − 0.064 ± 0.007 and − 0.063 ± 0.008 PgC yr −1 decade −1 these trends are of comparable magnitude to estimates from surface ocean p CO 2 -based flux products, but they are larger, by a factor of 3–4, than trends estimated from global ocean biogeochemistry models.