Climate impacts on the structures of the North Pacific air-sea CO₂ flux variability

Abstract. Some dominant spatial and temporal structures of the North Pacific air-sea CO₂ fluxes in response to the Pacific Decadal Oscillation (PDO) are identified in three data products from three independent sources: an assimilated CO₂ flux product and two forward model solutions. The interannual variability of CO₂ flux is found to be an order of magnitude weaker compared to the seasonal cycle of CO₂ flux in the North Pacific. A statistical approach is employed to quantify the signal-to-noise ratio in the reconstructed dataset to delineate the representativity errors. The dominant variability with a signal-to-noise ratio above one is identified and its correlations with PDO are examined. A tentative four-pole pattern in the North Pacific air-sea CO₂ flux variability linked to PDO emerges in which two positively correlated poles are oriented in the northwest and southeast directions and contrarily, the negatively correlated poles are oriented in the northeast and southwest directions. This pattern is identified in three products, providing CO₂ and pCO₂. Its relations to the interannual El Niño-Southern Oscillation (ENSO) and lower-frequency PDO are separately identified. A combined EOF analysis between air-sea CO₂ flux and key variables representing ocean-atmosphere interactions is carried out to elicit robust oscillations in the North Pacific CO₂ flux in response to the PDO. The proposed spatial and temporal structures of the North Pacific CO₂ fluxes are insightful since they separate the secular trends of the surface ocean carbon from the interannual variability. The regional characterization of the North Pacific in terms of PDO and CO₂ flux variability is also instructive for determining the homogeneous oceanic domains for the Regional Carbon Cycle and Assessment Processes (RECCAP).