Land Surface Influence on Boundary Layer Air over the Atlantic Ocean from Environmental Radioactivity

Abstract This study addresses the variability of gamma radiation measurements over the Atlantic Ocean. The analysis of back trajectories shows that the path of the air masses is the main factor determining gamma radiation levels over the ocean, rather than the distance to the coast. Different gamma values were recorded at different times in the same location as a result of the distinct origin of the corresponding air masses. Higher counts observed in the northeast Atlantic in winter compared with the spring values result from air masses coming from Europe and the African continent. In general, gamma radiation values over the ocean increase with increasing continental influence on the air mass above. A predictive classification model is developed showing that marine gamma observations can be used to classify marine boundary layer air masses according to the degree of continental influence. Significance Statement The atmosphere above the ocean plays a fundamental role in Earth’s climate, but direct observations of marine air are scarcer and more challenging than land-based measurements. In this study, we consider gamma radiation emitted by naturally occurring radionuclides, which serves as a proxy for dynamic environmental processes. We investigate the variability of gamma radiation in marine air from direct ship-based measurements over the Atlantic Ocean. We find that gamma radiation levels are mainly determined by the history of the marine air masses and the proportion of their previous land contact. Thus, gamma radiation over the ocean reflects the degree of continental influence on marine air masses, which is crucial information to improve understanding of atmospheric transport processes.