Tracing climate-driven shifts in Arctic microbial eukaryotes over the past ~900,000 years using sedimentary ancient DNA

Predicting how Arctic marine biodiversity will respond to climate change remains a major challenge in the natural sciences, largely as adaptive processes like changing phenology or behavior are difficult to model. An alternative approach to understanding climate-biota dynamics involves analyzing molecular traces of past life – sedimentary ancient DNA (sedaDNA) – preserved in marine sediments. This method allows us to study the long-term responses of Arctic marine biodiversity to climate and environmental dynamics up to geological timescales. By probing the past via sedaDNA, we aim to understand how climate-driven cryosphere dynamics have affected Arctic marine microbial eukaryotes and associated ecosystem functions over past glacial – interglacial cycles. We present first results of in-solution hybridization capture coupled with high-throughput sequencing to enrich for the typically underrepresented eukaryotic diversity preserved in the sediments of IODP Hole U1604B covering the past ~900,000 years. A wide range of protists was retrieved, including groups typically found in the marine microfossil record (e.g., diatoms, dinoflagellates, foraminifera, haptophytes) but also of many groups that are usually absent (e.g., ciliates, apicomplexans, chlorophytes). We observed marked contrasts in sedaDNA preservation and microbial eukaryote diversity between glacial and interglacial periods, indicating that past episodes of intense glaciation and cooling strongly shaped microbial eukaryote communities. Our preliminary findings pave the path for reconstructing Arctic ecosystem sensitivity across multiple glacial–interglacial transitions, offering a powerful framework for projecting how marine biodiversity may respond to future climate-driven cryosphere change.