1.Overview

Nitrogen compounds emitted from East Asia, including atmospheric PM2.5 aerosol particles*, play a significant role in increasing the amount of phytoplankton in the western North Pacific subtropical area. This new result was determined by numerical simulations and satellite data analysis in a study led by Dr. Fumikazu Taketani of the Research and Development Center for Global Change at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC: Asahiko Taira, President) in cooperation with Kobe University and the National Institute for Environmental Studies.

Nutrients such as nitrogen compounds, which control the amount of phytoplankton near the ocean’s surface, are mostly supplied by deep ocean circulation (Figure 1). However, in the western North Pacific subtropical area, the amount of nutrients supplied to the ocean’s surface in this manner is extremely small, indicating the importance of nutrients sourced from the atmosphere instead. Until now, the effects of the nutrient supply process from the atmosphere have only been estimated based on the amount of nutrients deposited into the ocean; quantitative evaluations considering marine ecosystems as well have not been previously undertaken.

To better understand this process, the research team developed improved numerical models by combining atmospheric chemical transport models and marine ecosystem models. Next, they ran these models on JAMSTEC’s Earth Simulator supercomputer to accurately estimate the response of phytoplankton in the western North Pacific to deposition of nitrogen compounds emitted in East Asia (Figure 2).

The results show that the amount of phytoplankton near the surface of the western North Pacific subtropical area is 2.3 times larger when the supply of nitrogen compounds from the atmosphere is taken into consideration, consistent with the estimations from satellite analysis (Figure 3). This indicates that the nitrogen compounds in PM2.5 are likely to play an important role in increasing the amount of phytoplankton in the western North Pacific subtropical area. These findings are the first to clarify this direct relationship between atmospheric matter and marine ecosystems.

Dr. Taketani says, “With the accumulation of more observation data, we will continue further investigations to identify how changes in the absorption of carbon dioxide and the amount of zooplankton are influenced by the supply of atmospheric nitrogen compounds.”

The above work was supported by JPS KAKENHI Grant Numbers JP15H05822, JP23241013, JP26340071, JP16H04051, JP18H03369, and JP18H04143, as well as a Research Grant from Asahi Group Foundation and the joint research program of the Institute for Space-Earth Environmental Research, Nagoya University.

The above results were published in Scientific Reports on June 29, 2018 (JST).
Title: Seasonal Response of North Western Pacific Marine Ecosystems to Deposition of Atmospheric Inorganic Nitrogen Compounds from East Asia

Authors: Fumikazu Taketani1, Maki N. Aita1, Kazuyo Yamaji2,1, Takashi Sekiya1, Kohei Ikeda3, Kosei Sasaoka1, Taketo Hashioka1, Makio C. Honda1, Kazuhiko Matsumoto1, and Yugo Kanaya1
Affiliations: 1JAMSTEC 2Kobe University 3National Institute for Environmental Studies