[A-AS21] Atmospheric Chemistry

[AAS21-18] Relationship between interannual variation in the changing rate of APO trend at Cape Ochi-ishi and PDO

*Yasunori TOHJIMA¹, Hitoshi MUKAI¹, Toshinobu MACHIDA¹, Yukio TERAO¹ (1.National Institute for Environmental Studies)

Keywords:APO, atmospheric oxygen, PDO, atmospheric CO2, air-sea gas exchange

Since atmospheric potential oxygen (APO=O₂+1.1xCO₂) mainly reflects the air-sea gas exchange of O₂ and CO₂ by definition, the spatio-temporal variations in APO are expected to constrain the ocean biogeochemical process and dynamics. Here we examine the relationship between temporal variations in APO trend observed at Cape Ochi-ishi (COI; 43.2^oN, 145.5^oE) and the Pacific Decadal Oscillation (PDO) index to investigate the causes for the inter-annual variations in the APO trend. The PDO is a long-term Pacific climate variability, having two extreme phases which is classified by basin-scale patterns of the sea surface temperature (SST) anomaly. When the SST anomalies are cool in the northern North Pacific and warm in the tropical Pacific, the PDO index has positive value. And the opposite pattern of the SST anomalies correspond to the negative PDO index. The cool SST enhances the ocean vertical ventilation which brings deeper waters with depleted O₂ to the surface, causing the O₂ ingassing. The cool SST also enhances the ingassing flux by increasing gas solubility. To the contrary, the enhanced ocean vertical ventilation brings the subsurface nutrients to the surface, enhancing the O₂ outgassing through the increase in the ocean primary production. Thus, the correlation analysis between the changing rate of the APO trend (dAPO/dt) at COI and the PDO index would allow us to investigate how the SST anomaly in the northern North Pacific affect the air-sea gas exchanges. Unfortunately, there is no significant correlation between dAPO/dt and the POD index. However, when dAPO/dt and the PDO index are decomposed into the middle (0.3