Investigation of the concentrations and fluxes of potent greenhouse gases (N2O, CH4, and CO2) in the port and harbor seawaters of Jeju Island, Korea.

Quantifying greenhouse gas (GHG) emissions from coastal environments is essential for understanding their role in climate change. Ports and harbors, which are semi-enclosed coastal systems, often experience nutrient accumulation from human activities, leading to GHG emissions. Jeju Island, with numerous ports and harbors along its coast, provides an ideal location for studying GHG emissions in these environments. This study investigates the spatial distribution, air-sea fluxes, and radiative forcing of N2O, CH4, and CO2 in Jeju's port and harbor waters during the summer of 2021. Sampling sites were classified into four categories based on dominant industry: Urban, Aquaculture, Nature tourism, and Agriculture. Greenhouse gas concentrations varied by region, with elevated N2O in urban and CH4 in tourism regions, while pCO2 was relatively low in both due to biological uptake. Additionally, Jeju's ports and harbors acted as a source of N2O, CH4, and CO2 to the atmosphere, with average fluxes of 1.67 ± 1.41 μmol m-2 d-1, 10.30 ± 10.24 μmol m-2 d-1, 0.16 ± 0.78 mmol m-2 d-1, respectively. Radiative forcing calculations indicated that while dissolved N2O levels were still low to exhibit radiative forcing, CH4 exhibited positive forcing only in the tourism region where concentrations were elevated, and CO2 concentrations were sufficiently high to exhibit radiative forcing. These findings highlight the importance of port and harbor environments as hotspots of coastal GHG emissions.