[A-CG44] Biogeochemical linkages between the surface ocean and atmosphere

[ACG44-P04] Modelling regional and global scale impacts of atmospheric nitrogen inputs on marine biogeochemistry

*Maki Noguchi Aita¹, Fumikazu Taketani¹, Yoko Iwamoto², Tomohiro Hajima³ (1.Earth Surface System Research Center, Japan Agency for Marine-Earth Science and Technology, 2.Hiroshima University, 3.Research Center for Environmental Modeling and Application, Japan Agency for Marine-Earth Science and Technology)

Keywords:atmospheric aerosol, nitrogen deposition, ocean biogeochemical cycle, primary production, marine ecosystem model

The spatio-temporal distribution and seasonality of oceanic primary producers may be altered by various external factors, including atmospheric deposition of anthropogenic aerosols, rising water temperature, increasing frequency of typhoons, and changing ocean mixing due to global warming (e.g., IPCC AR5). Primary producers in the surface ocean are sustained by nitrogenous nutrients supplied via five main processes: nitrification, vertical mixing, nitrogen fixation, atmospheric aerosol deposition (including rainfall), and inflows from rivers. Over the last several decades, atmospheric aerosol emissions from East Asia have increased rapidly. However, the effects of "atmospheric aerosols" on primary producers have not yet been well quantified (e.g., Steffen et al., 2015). To investigate the impact of atmospheric nitrogen deposition on primary producers, we conducted simulations using a marine ecosystem model combined with an atmospheric chemistry transport model. Our results showed that aerosol deposition enhanced primary production in the surface ocean by a factor 1.7 in the subtropical North western Pacific (Taketani et al., 2018). This is because aerosol deposition has enhanced the supply of essential nutrients such as nitrogen, phosphorus and iron, which typically limit production under natural conditions near the ocean surface. Statistical analyses of observed sea surface nutrient concentrations in the North Pacific over the past 50 years have revealed decreasing trends for phosphate and silicate concentrations, whereas no significant trend was detected for nitrate concentration (Yasunaka et al., 2016). The lack of a clear trend for nitrate may reflect the net effect of increased anthropogenic nitrogen sources combined with reduced supply of nitrogen from deep waters as mixed layer depths have decreased due to global warming. We will review previous studies using marine ecosystem models and Earth System Models, focusing on the effects of atmospheric nitrogen inputs on marine biogeochemistry during short- and long-term climate change and global warming.