Estimation of CH₄ emissions from the East Siberian Arctic Shelf based on atmospheric observations aboard the R/V Mirai during fall cruises from 2012 to 2017

Atmospheric CH₄ mole fractions were observed aboard the R/V Mirai sailing in waters off Alaska in the Arctic Ocean in September 2012–2017 to investigate the CH₄ emissions from the surrounding region, especially from the East Siberian Arctic Shelf (ESAS). The synoptic-scale increases of CH₄ were compared with simulated increases based on a Lagrangian Particle Dispersion Model and monthly CH₄ flux maps determined by a global atmospheric inversion system. There were good agreements between the observed and simulated CH₄ increases, suggesting the validity of CH₄ fluxes from the surrounding areas of the cruise experiments. The CH₄ emissions from the ESAS in September were further optimized in order to minimize the root mean square of the differences between the observed and simulated CH₄ increases. The average (±1σ) of the resulting emission rates was 0.58 ± 0.47 TgCH₄ yr⁻¹, which was much smaller than previously reported estimates. The individual optimized CH₄ emissions varied from −0.1 ± 0.3 to 1.3 ± 0.4 TgCH₄ yr⁻¹, showing a positive correlation with the sea surface temperature and a negative correlation with the ice concentration of the ESAS area in September. These results suggest a possible enhancement of the CH₄ emissions from the ESAS in a warmer future.