Air-sea CO₂ Fluxes And Controlling Factors In The Marginal Seas And Western North Pacific Ocean

Global climate change caused by the increase of greenhouse gas concentrations has been recognized as a common human concern,wherein carbon dioxide?CO₂?significantly contributes to the global warming.The ocean plays a crucial role in regulating atmospheric CO₂ levels and determines the concentration of atmospheric C02.At present,there is a general understanding of the distribution pattern of global ocean carbon sources and sinks.However,there exists a large uncertainty in precise estimating global C02 flux due to the limited field survey data from time and space.It is more difficult for marginal seas because of significant regional differences and seasonal variations.In this study,underway observations of sea surface pCO₂ were conducted in four typical tropical and subtropical margin seas?Taiwan Strait,South China Sea?,and one open ocean area that is subtropical waters in the Western North Pacific Ocean.The distribution of sea surface pCO₂ was examined and the pattern of CO₂ source or sink was evaluated.Moreover,air-sea CO₂ fluxes were estimated.The effects of various environmental factors and El Nino-La Nina events on sea surface pCO₂ and air-sea CO₂ fluxes were discussed.The main conclusions were as follows:1 Taiwan Strait?1?Sea surface pCO₂ in the Taiwan Strait had large spatial variation and seasonal fluctuation,and there was an increasing trend year by year.?2?According to the results of this study and historical literatures,Taiwan Strait served as a sink for atmospheric CO₂ in winter and spring.In contrast,it acted as a source of atmospheric CO₂ or is in equilibrium with atmospheric CO₂.2 South China Sea?1?In the northern South China Sea,the complex factors affected the distributions of temperature and salinity.Sea surface pCO₂ and air-sea CO₂ fluxes therefore showed large temporal and spatial variations.The south-central South China Sea was characterized of high temperature throughout the year,thereby,sea surface pCO₂ in the main area was mainly controlled by temperature.The sea surface pCO₂ and air-sea C02 fluxes in the South China Sea had large interannual variability and behaved increasing trend year by year.?2?Except the shelf area of the northern South China Sea become the sink of atmospheric CO₂ or approached to equilibrium with atmospheric CO₂ in the late autumn to winter,in the other seasons the various area of the South China Sea become the source of atmospheric CO₂.Air-sea CO₂ flux during La Nina event was 5-fold higher than that during El Nino event.3 Western North Pacific OceanIn May and September 2014,sea surface pCO₂ in the subtropical waters of the western North Pacific Ocean has significant changes with season and latitude.In May,the observed sea areas become a sink of atmospheric CO₂ and air-sea C02 flux was-1.53 mmol m-2 d-1.While,in September it showed a source of atmospheric CO₂ with air-sea C02 flux of being 1.55 mmol m-2 d-1.To sum up,a large number field observed data for underway sea surfacePCO₂ and other relative parameter were obtained from aforementioned five sea areas in various seasons,which enriched the data base of sea surface pCO₂ in above-mentioned marginal seas and open ocean.and provided data support and technology development for precise estimating of regional and global air-sea CO₂ fluxes.