Variability of North Atlantic CO₂ fluxes for the 2000–2017 period

Abstract. We present new estimates of the regional North Atlantic (15° N–80° N) CO₂ flux for the 2000–2017 period using atmospheric CO₂ measurements from the NOAA long term surface site network in combination with an atmospheric data assimilation system (GEOSChem–LETKF). We also assess the sensitivity of flux estimates to the representation of the prior ocean flux distribution and to the associated specification of prior flux uncertainty, including a specification that is dependent on the agreement among the multiple representations of the prior ocean flux. Long term average flux estimates for the 2000–2017 period are −0.26±0.04 PgC y⁻¹ for the subtropical basin (15° N–50° N), and −0.25±0.04 PgC y⁻¹ for the subpolar region (50° N–80° N, west of 20° E). Our basin–scale estimates of the amplitude of interannual variability (IAV) are 0.037±0.006 PgC y⁻¹ and 0.025±0.009 PgC y⁻¹ for subtropical and subpolar regions respectively. We find a statistically significant trend in carbon uptake for the subtropical North Atlantic of −0.062±0.009 PgC y⁻¹ decade⁻¹ over this period.