Volatiles in the mantle below Northern Antarctica: Insights from Deception Island volcano

The incomplete knowledge of the pristine composition of the Earth’s interior along with the variable impact of shallow ecosystems on the mantle over geological time severely restrict the ability to assess the volatiles budget in the Earth’s deep reservoirs and how geodynamics controls mantle heterogeneity. We present the results of a geochemical exploration at Deception Island volcano in Antarctica, whose fluids provide the rare opportunity to investigate the mantle at very high latitudes. This region is characterized by a paucity of data due to its remoteness and not easy to reach to explore and collect samples in the field. Helium isotopes combined with the carbon-isotope composition of carbon dioxide in fluids emitted at Deception Island match the composition of the convective Mid Oceanic Mantle Reservoir (MORB-type). In contrast, the nitrogen 15 N 15 N isotopologues surprisingly indicate an excess of nitrogen respect to a MORB-type Earth mantle. We conclude that this is due to the subduction of shallow crustal materials with low carbon/nitrogen ratios—typical of high-latitude regions—down into the mantle. Our results therefore highlight the impact of the surface environment on the Earth’s interior by revealing a convincing match between the low carbon/nitrogen ratios of the lowest latitude surface environment and of the mantle-derived fluids. These findings offer novel perspectives into the role of diverse latitudinal surface ecosystems in shaping the heterogeneity of the Earth’s mantle and their implications for carbon and nitrogen cycles.