Low frequency changes in CO concentration in East Asia related to Pacific decadal oscillation and Atlantic multi-decadal oscillation for mid-summer and early fall.

The climatological seasonal maximum and minimum CO concentrations in East Asia for 1987-2020 have been recorded at April and August, respectively. We found that the CO concentration in East Asia during July, August, and September (JAS) is lower than normal before the late 1990s and after the early 2010s (Low_CO period), and higher than normal from the late 1990s to the early 2010s (High_CO period). The low-frequency variability of CO concentration in East Asia during JAS correlates with both Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO)-related sea surface temperatures (SSTs). We analyzed atmospheric and oceanic conditions during JAS between the two periods, finding that precipitation in East Asia decreased during JAS in High_CO period than that in Low_CO period, possibly due to PDO and AMO-related SST forcing, which decreases vegetation's photosynthetic activity. This may lead to a higher CO concentration than normal in East Asia in High_CO period through reduced uptake of CO from the atmosphere. This implies that terrestrial vegetation activity influenced by remote SST forcings should be monitored to better understand regional carbon cycles in East Asia.