Extreme late-Holocene diatom biomarker enrichment reveals late-season ice-edge productivity in the Barents Sea

Sea ice plays a critical role in regulating Earth’s climate and marine productivity. Reconstruction of sea ice and productivity is generally achieved using biotic or geochemical proxies, although methods targeting the late-season sea-ice minimum and associated productivity remain elusive. Here, we identified extreme sedimentary enhancements of two diatom biomarker lipids (HBI III, HBI IV) in a high-resolution core from the northern Barents Sea at a time during the mid to late 19th century when the summer sea-ice minimum was located directly over the core site. We attribute this enhancement to a late-summer ice-edge diatom bloom, an interpretation supported by other biomarker, geochemical and ocean temperature data. Such blooms were likely dominated by diatoms (Rhizosolenia spp.), which can access nutrients below the nutricline via vertical migration. Our findings provide insights into the role of sea ice on marine productivity and a potential means of identifying the sea-ice minimum in palaeo records. Intense diatom blooms indicate late-season sea-ice edges in sedimentary records, according to biomarker analysis of a high-resolution core from the northern Barents Sea.