Asian dust-deposition flux to the subarctic Pacific estimated using single quartz particles.

Iron availability limits marine ecosystem activities in large areas of the ocean. However, the sources and seasonal supply of iron, critically important for controlling surface ocean biogeochemistry and carbon cycling, are poorly understood. The western subarctic Pacific is a high-nutrient and low-chlorophyll region, and despite high concentrations of macronutrients, iron limits phytoplankton production in summer. Here, we determine the seasonal deposition flux of Asian dust using scanning electron microscope-cathodoluminescence analysis of single quartz particles derived from the western subarctic Pacific during 2003-2022 to trace provenance. We found a high (up to 6.9 mg m day) deposition flux of Asian dust in May, June, and early July, with an annual average of 1.0 ± 0.2 mg m day. The supply of dissolved-iron flux calculated from Asian dust was 0.9 ± 0.3 µg m day during the high productivity season (April-July), which is approximately half that from the deeper part of the ocean, calculated from vertical profiles of dissolved iron. Our study provides a reliable approach for estimating iron supply from dust to the surface ocean that may be critical for sustaining biological productivity under future ocean stratification, which suppresses nutrient supply from the subsurface ocean.