Methane in the Yellow Sea and East China Sea: dynamics, distribution, and production

The Yellow Sea (YS) and East China Sea (ECS) are important marginal seas of the western Pacific. Understanding the dynamics of methane (CH4) in the YS and ECS are essential to evaluate the role of coastal seas in global warming. We measured dissolved CH4 at various depths in the water column of the YS and ECS during a cruise from March to April 2017. The concentrations of CH4 varied greatly in different water masses, suggesting that the hydrographic conditions can substantially affect the CH4 distribution. The CH4 budget in the shelf of the ECS, which was estimated with a box model, suggests CH4 consumption in the water column was the major sink (>95%), followed by a loss with a total of 2.2% CH4 released to the atmosphere. Overall a local CH4 production of 0.28 nmol/(L center dot d) was needed to maintain the CH4 excess. Results from laboratory incubations showed an increase in CH4 (1.5 times higher than the value of the control) after the addition of dimethylsulfoniopropionate (DMSP). Field incubations result in a CH4 production rate of 1.2 nmol/(L center dot d) under a N-stressed conditions (N:P<1), indicates that the DMSP-dependent CH4 production prefer to occur in the oligotrophic seawaters, where nitrogen is depleted. This study demonstrates that the marginal seas of China is a hotspot for CH4 dynamics, and the cycling of methylated sulfur compounds (such as DMSP) may contribute importantly to locally formed CH4. This may have further implication to carbon and sulfur biogeochemical cycles in the western Pacific.