Details

Autor(en) / Beteiligte

• He, Wenbo
• Lai, Zhigang
• Lu, Wenfang
• Li, Dongdong
• Chen, Changsheng

Titel

The Effects of Atmospheric Nitrogen Deposition on the Marine Ecosystem of the Northern South China Sea

Ist Teil von

• Journal of geophysical research. Oceans, 2023-01, Vol.128 (1), p.n/a

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2023

Quelle

Wiley Online Library

Beschreibungen/Notizen

• The rapid economic developments in countries surrounding the South China Sea have caused a significant increase in the atmospheric deposition of nitrogen (AD‐N) into the ocean. The impact of AD‐N on the regional ecosystem has not been quantitatively assessed, and its driving mechanism has not been explored, either. Here, we applied a one‐dimensional European Regional Seas Ecosystem Model to examine the responses of the ecosystem to AD‐N. The physical‐biological coupled model reproduced the seasonal and interannual variabilities of observed nutrients, chlorophyll a, phytoplankton community structure, and particulate organic carbon (POC) exports at the South East Asia Time‐series Station. Seasonally, the increase of POC flux by AD‐N was most significant in winter, with a ∼2‐month lag behind the associated surface response. It can exist in the following spring, as supported by the larger population size of zooplankton after the previous winter's feeding up. Notably, the ratio of POC export to primary production varied seasonally and interannually, which was controlled by the phytoplankton and zooplankton's size compositions. The surface nutrient input thus caused a significant seasonal change in the biological carbon pump efficiency. Interannually, the modulation of the POC flux by AD‐N was inversely phase‐locked with wind variations. The out‐of‐phase of the surface‐ and subsurface‐nutrient‐driven POC fluxes suggested a potentially more considerable contribution of AD‐N to the total carbon export during years under the weak subsurface influence. This study highlights the importance of AD‐N in the regional ecosystem, which needs a better representation in the present biogeochemical modeling framework. Plain Language Summary The atmospheric deposition of nitrogen (AD‐N) to the ocean, by human fertilizer usage and fossil fuel combustion, has significantly impacted the offshore marine ecosystem. The northern South China Sea (NSCS) is a hot spot of such influence because it is surrounded by countries with rapid economic development and gigantic emissions. The added nutrients from the terrestrial sources then can be rapidly assimilated into the primary production since the surface water of the NSCS is seasonally nutrient‐depleted. Numerical simulations were conducted to gain insights into the influence of AD‐N on the seasonal change in biogeochemistry and the consequence of carbon export. The results showed that the AD‐N could lead to a more substantial growth response in the portion of the tiniest picophytoplankton group and a subsequent increase in carbon export. The influence has a persistent impact on the ecosystem until the following spring and causes a decrease in the biological carbon pump's efficiency in autumn. Interannually, the AD‐N could contribute more to the export carbon flux during weaker wind and lower nutrient concentration conditions. Our findings highlight the vital roles of AD‐N in the food web system, which were not systematically quantified previously and should be represented in future modeling frameworks. Key Points A new physical‐biological coupled model with atmospheric deposition of nitrogen (AD‐N) was established The carbon export efficiency varied with phytoplankton size structure, and the variation could be up to 30% Impacts of the AD‐N on the particulate organic carbon flux were more significant during weak wind conditions