Sea animals promote carbonyl sulfide (OCS) emissions from Antarctic tundra

Carbonyl sulfide (OCS), the most abundant atmospheric sulfur-carrying gas, can contribute to regulating Earth’s radiative balance through forming sulfate aerosols. The bryophyte-dominated tundra lying over the ice-free Antarctica is an important terrestrial carbon sink and provides colonies for sea animals, such as penguins and seals, which remains hitherto unexplored concerning OCS biogeochemistry. Here, we measured OCS fluxes from the Antarctic tundra and coupled their fluxes to soil biogeochemical properties to explore OCS production and degradation processes. The bryophyte-dominated normal upland tundra was an OCS sink at -0.97 ± 0.57 pmol m^-2 s^-1, resulting from both bryophytes and OCS-metabolizing enzymes (e.g., carbon anhydrase, nitrogenase) secreted by soil microbes, such as Acidobacteria, Verrucomicrobia, Chloroflexi, and Mortierellomycota. In comparison, tundra within sea animal colonies was an OCS source up to 1.35 ± 0.38 pmol m^-2 s^-1, due to the input of organosulfur from sea animals and the animal-induced anaerobic soil environment, which promoted simultaneous abiotic OCS production in soil, and outweighed the biogenic OCS uptake by bryophytes and soil microbes. Furthermore, sea animal colonization shaped the soil microenvironment, affecting nutrient levels, pH and moisture, which may have reduced the abundances of OCS-metabolizing microbes and thereby OCS degradation and further unveiled concurrent OCS production. Basic calculation suggested that sea animals contribute about 107 metric tons yr^-1 of OCS-S to the atmosphere. The strength of this OCS source is expected to increase in response to Antarctic warming. Overall, tundra ecosystems are important interfaces for OCS exchange and sea animals exert an impact on the sulfur cycle in coastal Antarctica.