Marine eukaryote community responses to the climate and oceanographic changes in Storfjordrenna (southern Svalbard) over the past ⁓14.0 kyr BP: Insights from sedimentary ancient DNA analysis

Abstract. Sedimentary ancient DNA (sedaDNA) metabarcoding is an emerging method to reconstructing the response of marine organisms to past climate and oceanographic changes, including rare and non-fossilized taxa. Marine sedaDNA records from the Arctic are scarce, especially those focusing on the impact of environmental shifts on the biodiversity and functional composition of marine eukaryote communities. Here, we present a sedaDNA eukaryotic record from the sediment core retrieved in Storfjordrenna, southern Svalbard, spanning the termination of the Bølling-Allerød, the Younger Dryas, and the Holocene (13.3–1.3 kyr BP). We successfully recovered the eukaryotic communities and identified them by their ecological roles. Our study showed that the eukaryotic biodiversity in Storfjordrenna remained relatively stable, except during transitions between major climatic intervals. These shifts were marked by changes in richness and relative abundance, driven by factors such as perennial ice cover, surface water cooling, and subsurface Atlantic water influx. Cercozoans and MAST emerged as dominant heterotrophs, characterized by high ecological flexibility and broad tolerance. The primary productivity was primarily driven by ArW-associated phytoplankton, including diatoms (Thalassiosira and Chaetoceros), green algae (Micromonas), and autotrophic dinoflagellates (Polarella glacialis,) as well as mixoplanktonic silicoflagellate Pseudopedinella elastica. The ASV-based indicator analysis revealed that uncultured Cercozoan lineages and MAST taxa were primarily associated with AW proxies, whereas parasitic dinoflagellates (Dino-group I) and choanoflagellates were more closely aligned with ArW proxies. The analysis of indicator responses shows the complex interactions within eukaryotic communities and reveals a strong association among functional ecological groups, which impacts ecosystem productivity and regulation. This complexity highlights the limitations of traditional single proxy approaches to accurately reconstructing paleoenvironmental conditions. Our study demonstrates the potential of high-resolution marine sedaDNA metabarcoding in elucidating responses to past climate changes and in improving our understanding of the intricate interactions within eukaryotic communities in marine ecosystems.