Sedimentary ancient DNA insights into foraminiferal diversity near the grounding line in the western Ross Sea, Antarctica

Abstract. Foraminifera are important marine environmental indicators widely used in paleoceanography and paleoclimate studies. They are a dominant component of meiobenthic communities around the Antarctic continental shelf, including rarely studied locations below the ice shelves, close to the grounding line. In this study, we use high-throughput sequencing of sedimentary ancient DNA (sedaDNA) targeting foraminifera with two molecular markers, including an ultrashort marker newly designed for this study, in five cores from the western Ross Sea, containing sediments up to 30 000 years old. No foraminiferal DNA is detected in the tills, suggesting a lack of preservation of sedaDNA during glacially induced sediment reworking and transport. We reconstruct diverse foraminiferal communities in the open-marine settings and significantly less diverse communities in sediments from the slopes of the sub-ice-shelf grounding-zone wedges, deposited proximal to the grounding line. Both assemblages are rich in soft-walled monothalamids not preserved in the fossil record and complement the results of earlier micropaleontological studies, allowing for a more complete reconstruction of past biodiversity. The newly designed minibarcode marker provides higher foraminiferal diversity in surface and subsurface samples than the standard barcode and allows for better differentiation between foraminiferal communities in different sediment types. It appears to have great potential for future paleoenvironmental studies, although its taxonomic resolution needs to be evaluated.