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

[ACG45-11] Asian dust-deposition flux to the subarctic Pacific and its Impact on the Phytoplankton Production

*Kana Nagashima¹, Hajime Kawakami², Koji Sugie¹, Fujiki Tetsuichi¹, Jun Nishioka³, Yoko Iwamoto⁴, Toshihiko Takemura⁵, Takuma Miyakawa¹, Fumikazu Taketani¹, Maki Noguchi Aita¹ (1.Japan Agency for Marine-Earth Science and Technology, Research Institute for Global Change, 2.Japan Agency for Marine-Earth Science and Technology, Research Institute for Value-Added-Information Generation, 3.Hokkaido University, Institute of low temperature sciences, 4.Hiroshima University, Graduate School of Integrated Sciences for Life, 5.Kyushu University, Research Institute for Applied Mechanics)

Keywords:Asian dust, Iron, Deposition flux, Primary production

The western subarctic Pacific is a high-nutrient, low-chlorophyll area, and iron is the limiting factor for primary production. Dust from Asian deserts is one of the major sources of iron in this region; however, its deposition flux, seasonality, and impacts on phytoplankton production have not previously been established.

Here we determine the seasonal concentrations of Asian dust in the mixed layer in this ocean region using an improved scanning electron microscope–cathodoluminescence (SEM–CL) analysis of single quartz particles collected from seawater in various seasons during 2003–2021. The results show high concentrations of Asian dust in spring and early summer in the western subarctic Pacific. In addition, we quantified the seasonal dust-deposition fluxes in the ocean. The estimated fluxes show high values of ca. 7 mg m⁻² day⁻¹ in early May, 2 mg m⁻² day⁻¹ in early June, and low values in the other months. We validated our estimations using the results of numerical simulations and the atmospheric dust concentrations in the Aleutian Islands and established their similarities. Furthermore, we quantified the impact of dissolved-iron flux supplied by Asian dust on phytoplankton production in the western subarctic Pacific; The calculated dissolved iron flux was about 28 ± 9% of the iron requirement for the phytoplankton primary production in this region during spring and summer. The remaining iron requirement was supplied by anthropogenic aerosols and from the deeper part of the ocean. Since accelerated stratification associated with recent and future surface ocean warming reduces nutrient supply from the deeper part of the ocean to the euphotic zone, iron supply from the atmosphere will increase in importance in the future.