Tracing terrestrial organic matter dynamics in the subarctic North Pacific using sedimentary ancient DNA metabarcoding

The subarctic North Pacific serves as a critical repository for terrestrial organic matter, yet the limited taxonomic resolution of traditional isotope and biomarker proxies constrains our ability to identify both its source taxa and source regions. Therefore, the source and transport dynamics of terrestrial organic matter in this basin remain poorly understood. Here we use land-plant sedimentary ancient DNA (sedaDNA) metabarcoding as a high-resolution proxy to trace the taxonomic composition and continental source regions of terrestrial organic matter, performing a same-proxy comparison between marine sediment cores from off-Kamchatka and the Bering Sea and lake records from Siberia and Alaska. We obtained unprecedented taxonomic resolution of terrestrial plant signals in both marine sediment cores, revealing a persistent, taxonomically coherent assemblage dominated by riparian taxa (e.g. Salicaceae). The comparison between marine and lake records reveals that marine archives largely represent a nested subset of the regional terrestrial taxon pool, with riparian vegetation overrepresented and steppe-tundra herbs and conifers underrepresented relative to lakes. This reflects integration across catchments, with hydrological filtering further amplifying these abundance contrasts in marine archives. A few region-specific indicator taxa (e.g. Spiraea salicifolia and Shepherdia canadensis) could be identified, providing direct taxonomic evidence for continental source attribution. Across the glacial–deglacial–Holocene transition, land-plant DNA assemblages in marine records shifted significantly, capturing changes in source taxa. These shifts are accompanied by changes in the coupling between marine and lacustrine records, highlighting dynamic source–sink connectivity over time. Our results demonstrate the potential of sedaDNA as a high-resolution tool to trace terrestrial organic matter in high-latitude oceans, highlighting the need for expanded DNA reference databases and further research into taphonomic processes affecting DNA in marine sediments.