[A-CG46] Biogeochemical linkages between the surface ocean and atmosphere

[ACG46-03] Examining the impact of rainfall on primary productivity in the oligotrophic subtropical ocean

*Kazuhiko Matsumoto¹, Fumikazu Taketani¹ (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:aerosol deposition, P vs E curve experiment, nutrients in rainwater

Aerosols are rich in inorganic nitrogen compounds and are transported from the continents to the ocean by dry and wet deposition. Therefore, aerosol deposition is a pathway of nutrient supply in the ocean surface. In the oligotrophic subtropical region, the effect of aerosol deposition on the marine ecosystem is important because nitrate in the surface layer is almost depleted. However, there are few examples of field observations to verify the effects of aerosol deposition on the marine ecosystem. In this study, we tried to examine the effects of aerosol deposition by focusing on rainfall, which is thought to have a large deposition effect. During the observation cruise conducted in March 2021 in the oligotrophic western North Pacific subtropical ocean, rain clouds were tracked by using Doppler radar and the P vs E curve experiments were conducted in the surface layer to measure primary productivity before and after rainfall. Although we could not necessarily detect the increase of nutrients in the seawater evidently, we found that the rainwater sample contained high concentrations of nitrogenous nutrients. And from the P vs E curve experiments, we confirmed that primary productivity was enhanced after rainfall at the surface. It was 1.5 times higher than that before rainfall in terms of daily primary production. We have demonstrated through field observations that rain-induced aerosol deposition has a significant impact on primary productivity in oligotrophic subtropical waters.