[A-CG45] Biogeochemical linkages between the surface ocean and atmosphere

[ACG45-P05] Impact of Atmospheric Nitrogen Nutrient Dry Deposition on Surface Primary Productivity over the subtropical western North Pacific

*Fumikazu Taketani¹, Kazuhiko Matsumoto¹, Takashi Sekiya¹, Kazuyo Yamaji^1,2, Yugo Kanaya¹ (1.Japan Agency for Marine-Earth Science and Technology, 2.Kobe University)

Keywords:biogeochemical cycle, dry deposition, surface primary productivity, nutrients

Wet and dry deposition processes of airborne natural and anthropogenic substances transported from continents to the ocean surface can be important pathways for supplying nutrients to the phytoplankton biomass, besides upwelling and river discharge. It is well known that the subtropical western North Pacific has always been a nutrient-depleted area, and atmospheric species from East Asia are also transported to this region, suggesting the possibility that the enhancement of surface primary productivity by the nutrients supplied from the atmosphere is observable. To investigate the influence of deposition of atmospheric nutrients (e.g., nitrogen compounds) on the marine ecosystem, we performed shipboard experiment for Photosynthesis–irradiance (PE) curve by sampling the surface water and estimated the impact of the nitrogen nutriments deposition derived from model simulations.
The PE curve experiments using surface seawater (0m) from bucket sampling were carried out at Station KEOS (25N,145E), Station 13(25.0N,135E), and Station 14 (28.5N,135E) during R/V Mirai cruise (MR21-01) on Mar.2021. We also measured nutrients and Chl-a concentration in the sampled sea water. Also, we estimated the atmospheric nutrients (nitrogen compounds) deposition flux at each Station using atmospheric chemical transport model (WRF-CMAQ).
The concentration of nitrogen compounds for NO3 and NH4 in the surface seawater at all stations were < 0.1 mmol/L, suggesting the nitrogen-nutrients depleted condition. Primary productivity for surface seawater measured in the PE curve experiment was highest at Station14 and lowest at Station KEOS. Atmospheric nitrogen compounds deposition flux for the corresponding stations and timing estimated by WRF-CMAQ indicated that the nitrogen compounds dry deposition flux at Stations 14 and 13 were higher than those at Stations KEOS, suggesting the dry deposition could influence the higher primary productivity at Stations 14 and 13.