Abstract

Long-range transported dust across the North Pacific influences the climate by altering radiative forcing, affecting cloud properties as it acts as an ice nucleus, and impacting surface ocean biogeochemistry and carbon cycling through the supply of iron to the subarctic Pacific, a region characterized by high nutrients and low chlorophyll. Asian dust has for a long time been considered the dominant source of trans-Pacific dust; yet recent numerical simulations have revealed the frequent presence of Saharan dust in the upper troposphere over East Asia, highlighting its potential importance in North Pacific environments. However, owing to technical limitations in detecting diluted trans-Pacific Saharan dust and the lack of annual records identifying it over North America, the amount, frequency, and seasonality of Saharan dust transport across the North Pacific—as well as its climatic impact—remain unclear. To address this issue, we determined the provenance of trans-Pacific dust during 1985–1989 using scanning electron microscope–cathodoluminescence analysis of single quartz particles within an ice core from Mount Logan, southern Yukon Territory, Canada, combined with numerical simulations using the Integrated Massively Parallel Atmospheric Chemical Transport model. Ice core records showed that Asian dust is predominant during most seasons, whereas Saharan dust becomes dominant in winter. Numerical simulations showed that from spring to fall (1985–1989 averages), Asian dust accounted for 49–73% of the total deposition at Mount Logan, with notable Saharan contributions of 16–18%. In contrast, during winter, Saharan dust accounted for 44% of the deposition, primarily owing to a decrease in Asian dust deposition while Saharan dust deposition remained relatively high, thereby supporting the findings from Mount Logan records. Our results for the first time provide evidence of frequent transport of the Saharan dust across the North Pacific. Combined with the simulated vertical concentration of Saharan dust over the North Pacific, trans-Pacific Saharan dust may substantially influence high-altitude cirrus cloud formation and potentially affect North Pacific ecosystems through iron deposition. These findings indicate that Saharan dust over the North Pacific is considerably more significant than previously recognized.