講演情報
[ACG67-P03]Mt. Logan雪氷コアおよび数値シミュレーションから明らかになったサハラ起源ダストの太平洋横断輸送
*長島 佳菜1、東 久美子2、伊藤 彰記1、平林 幹啓2、白岩 孝行3、的場 澄人3、瀬川 高弘4、 金森 晶作5、永塚 尚子1 (1.国立研究開発法人海洋研究開発機構 、2.国立極地研究所、3.北海道大学、4.山梨大学、5.とかち鹿追ジオパーク推進協議会)
キーワード：
サハラダスト、アジアダスト、アイスコア、ダストモデル、石英、カソードルミネッセンス
Ice cores from Mount Logan in the southern Yukon Territory, Canada, offer a rare archive for assessing trans-Pacific transport of dust on seasonal to centennial timescales. The magnitude, timing, and source regions of dust reaching the North Pacific are key to understanding atmospheric composition and radiative balance (e.g., Gong et al. 2006), cloud microphysical processes through ice-nucleating activity (Stith et al. 2009), and marine biogeochemistry via iron supply to the subarctic Pacific Ocean (Tsuda et al. 2003). Trans-Pacific dust has traditionally been attributed primarily to Asian sources from the Taklimakan and Gobi Deserts, which together account for more than 10% of global dust emissions. In contrast, recent numerical simulations have suggested that Saharan dust—the largest global dust source, responsible for nearly half of worldwide emissions—is frequently present in the upper troposphere over East Asia, implying a potentially overlooked role in North Pacific environments.
Despite these model-based insights, the contribution of Saharan dust to the North Pacific remains poorly constrained because of difficulties in identifying highly diluted Saharan dust and the absence of annually resolved provenance records over North America. Here, we investigate the provenance, frequency, and seasonality of trans-Pacific dust transport during 1985–1989 by combining scanning electron microscope–cathodoluminescence analysis of single quartz particles from a Mount Logan ice core with numerical simulations using the Integrated Massively Parallel Atmospheric Chemical Transport (IMPACT) model. The ice-core record indicates that Asian dust dominates deposition during most seasons, whereas Saharan dust becomes the principal contributor in winter (Nagashima et al 2026, accepted). This seasonal contrast is reproduced by the IMPACT simulations, which show elevated wintertime Saharan dust deposition at Mount Logan, accounting for approximately 40 –50% of total dust deposition, largely due to reduced Asian dust input while Saharan dust fluxes remain high. During other seasons, Asian dust prevails, although Saharan dust still contributes substantially (approximately 15–20%) (Nagashima et al 2026, accepted).
These observations provide the first direct evidence for frequent transport of Saharan dust across the North Pacific. Together with simulated vertical distributions showing enhanced Saharan dust concentrations in the upper troposphere and estimated number concentration of ice-nucleating particles, our results suggest that trans-Pacific Saharan dust may play a substantial role in high-altitude cirrus cloud formation and potentially influence North Pacific ecosystems through iron deposition to the subarctic Pacific.
Despite these model-based insights, the contribution of Saharan dust to the North Pacific remains poorly constrained because of difficulties in identifying highly diluted Saharan dust and the absence of annually resolved provenance records over North America. Here, we investigate the provenance, frequency, and seasonality of trans-Pacific dust transport during 1985–1989 by combining scanning electron microscope–cathodoluminescence analysis of single quartz particles from a Mount Logan ice core with numerical simulations using the Integrated Massively Parallel Atmospheric Chemical Transport (IMPACT) model. The ice-core record indicates that Asian dust dominates deposition during most seasons, whereas Saharan dust becomes the principal contributor in winter (Nagashima et al 2026, accepted). This seasonal contrast is reproduced by the IMPACT simulations, which show elevated wintertime Saharan dust deposition at Mount Logan, accounting for approximately 40 –50% of total dust deposition, largely due to reduced Asian dust input while Saharan dust fluxes remain high. During other seasons, Asian dust prevails, although Saharan dust still contributes substantially (approximately 15–20%) (Nagashima et al 2026, accepted).
These observations provide the first direct evidence for frequent transport of Saharan dust across the North Pacific. Together with simulated vertical distributions showing enhanced Saharan dust concentrations in the upper troposphere and estimated number concentration of ice-nucleating particles, our results suggest that trans-Pacific Saharan dust may play a substantial role in high-altitude cirrus cloud formation and potentially influence North Pacific ecosystems through iron deposition to the subarctic Pacific.