Global ammonia emissions from seabirds.

Seabirds transport significant amounts of nitrogen from the ocean to the land in the form of excreta. The subsequent volatilization of nitrogen may result in significant emissions of atmospheric ammonia (NHs) in remote coastal systems. Blackall et aL, (2007) estimated global seabird NHa emissions to be 242 GgN year"1, however their emission estimate was not parameterised for all climate types and is based on old and potentially inaccurate historical population data. -- To update the global seabird NHs emission estimate, a contemporary seabird database of 261 million breeding seabird pairs was developed. This dataset was used in conjunction with a refined version of an existing seabird NHs model (GUANO) to estimate NHs emissions from seabirds in a range of climates. The estimate was further refined by using seabird habitat parameters that were validated through laboratory and field measurements. The field measurements, in various climate types, provide a more robust mechanism by which seabird emission factors could be validated for use in the global model A global seabird NHs emission estimate of 82 [37 - 127] Gg NHs year"1 is presented, with uncertainty as a result of variation in diet composition (± 23 %), non-breeder attendance (±13 %), ground temperature estimates (± 32 %) and seabird population estimates (± 36 %). -- Seabirds in the tropics are more significant emitters than previously thought, whilst emissions from polar regions were less significant than expected. The largest cafculated NHs emissions were on islands in the Southern Ocean and Pacific Ocean, with a maximum colony emission of 3.9 Gg NHs year"1 from the Sooty tern colony on Baker Island, Pacific Oceaa These NHs emissions are environmentally relevant, as they primarily occur as "hot-spots" in otherwise nutrient-free regions and may play a fundamental ecobgical and biogeochemical role in these ecosystems.