Spatial and temporal variation of methane emissions in the coastal area of Majorca and Cabrera

Trabajo presentado en el ASLO Aquatic Sciences Meeting, celebrado de forma virtual del 22 al 27 de junio de 2021Methane (CH4) is the second most important greenhouse gas after carbon dioxide (CO2), and is responsible for approximately 20% of the radiative forcing by well-mixed greenhouse gases in the lower atmosphere. In oceanic systems, shelf regions and estuaries are a minor source of atmospheric CH4 emitting around 2.3 - 15.6 Tg CH4 yr -1, while their contribution is probably higher due to sedimentary sources in coastal areas. However, these estimates show high uncertainties and seasonal variability, and results are mostly limited to the specific study area, especially in marginal areas. In this study, we sampled a range of three different locations along the Mallorca coast, including the archipelago of Cabrera (Bay of Palma, Cap Ses Salines, and Cala Santa Maria in PN Cabrera). Samples are taken from surface water and apart from CH4 additional variables were monitored such as temperature, salinity, DOC, alkalinity, and Chl a. To determine water-atmosphere fluxes, we used the transfer coefficient and the difference in concentrations between water and atmospheric values. The samples presented a concentration range of 2.7 - 4.5 nmol L -1 CH4 with an average of 3.9 nmol L -1. Fluxes were seasonal with the highest flow estimates for summer whereas the lowest estimates were obtained in winter. Finally, we determined the relationship between different environmental variables and their effect on the estimation of CH4 fluxes and discuss spatial patterns