Monthly Resolved Coral Ba/Ca Evidence for a Post‐Little Ice Age Decline in East Asian Dust Delivery to the Western Pacific

Abstract Asian dust storms influence climate, air quality, and nutrient supply, yet debate persists over whether their activity peaked during the cold Little Ice Age (LIA, ∼1550–1850 CE) or in the warmer, land‐use‐intensive modern era. Existing reconstructions derive mainly from loess, lake, and ice‐core archives; these capture aspects of dust activity but suffer from chronological uncertainty. High‐resolution downwind marine records at subannual scales remain scarce. We analyzed monthly barium‐to‐calcium (Ba/Ca) ratios in a Porites coral core from the Xisha Islands in the South China Sea (SCS), generating the first monthly resolved marine record of downwind dust‐associated aerosol delivery to the SCS during 1816–2014 CE. After excluding the influences of fluvial input, groundwater, upwelling, sediment resuspension, biological processes, and skeletal growth‐rate effects, we interpret the March–May Ba/Ca spikes as signatures of Ba‐rich aerosols delivered during spring dust activity. A Pettitt change‐point test identified 1870 as the boundary between two regimes: during 1816–1870, the mean spring Ba/Ca was 14.69 μmol mol −1 (vs. 10.47 μmol mol −1 thereafter), the variance was greater (3.44 vs. 2.24), and extreme events (>16.49 μmol mol −1 ) occurred in 31.5% of years (vs. 1.5% after 1870); all differences are significant. The post‐1870 decline in dust delivery parallels a weaker Siberian High, wetter upwind conditions, and fewer El Niño events, with no sustained anthropogenic increase in long‐range dust delivery to the SCS. These findings underscore climate forcing as the primary regulator of long‐range dust export and provide a precisely dated benchmark for testing aerosol–climate models and future dust–climate feedbacks.