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

Abstract. The subarctic North Pacific receives and preserves substantial amounts of terrestrial organic matter, yet the limited taxonomic resolution of traditional isotope and biomarker proxies constrains our ability to identify its source taxa and source regions, leaving its provenance and transport dynamics poorly understood. Here we use land-plant sedimentary ancient DNA (sedaDNA) metabarcoding to trace terrestrial plant organic matter in marine sediment cores from off-Kamchatka and the Bering Sea. We achieved unprecedented taxonomic resolution for marine sedaDNA records, identifying 328 terrestrial plant taxa, including 173 resolved to species level, across the two marine cores. Comparison with Siberian and Alaskan lake sedaDNA records showed that terrestrial plant assemblages recovered from the marine cores broadly reflected regional vegetation patterns and their temporal changes, while contrasts in relative taxon abundances indicated taphonomic filtering in marine sedaDNA records. Compositional relationships between the marine and lacustrine records, together with Siberian- and Alaskan-associated indicator taxa (e.g., Spiraea salicifolia and Shepherdia canadensis), provided taxonomic evidence for regional source attribution. Across the glacial–interglacial transition, the two marine records preserved distinct regional vegetation histories. Diversity patterns differed between the sites, with the Bering Sea record more strongly influenced by deglacial terrigenous delivery and the off-Kamchatka record more closely associated with postglacial warming. Our results demonstrate the potential of targeted sedaDNA metabarcoding as a high-resolution tool for tracing terrestrial organic matter in high-latitude oceans and highlight the need for expanded DNA reference databases and improved understanding of marine sedaDNA taphonomy.