Assessing the impact of past environmental change on fjord biodiversity using sedimentary ancient DNA

Fjords are strongly affected by climate change and direct anthropogenic impacts. Their location at the land-ocean interface makes them particularly vulnerable to a wide range of stressors. Rapid changes, such as increasing water temperatures, changes in oxygen conditions, increased run-off from land and decreasing sea ice in the Arctic will inevitably have profound effects on marine biodiversity and productivity. However, so far, our knowledge on the impact of these changes on marine communities remains limited, despite their important roles in food webs and nutrient cycling. To understand ongoing and future changes in fjord ecosystems and the resilience of marine communities, it is essential to assess their response to past changes in environmental conditions. To date, such studies are limited to lineages with a fossil record, leaving an incomplete picture of the remaining diversity. To address this issue, in the project PASTIME we are now applying sedimentary ancient DNA as a new tool for reconstructing past changes in entire marine communities in relation with past environmental changes. We focus on marine sediment cores from Arctic and western Norwegian fjords and assess environmental and biodiversity changes over the last centuries. Our work extends the timescales far beyond traditional observational data and allows assessing the impact of various environmental factors (e.g. temperature, freshwater inflow, sea ice, oxygen) under in-situ conditions to elucidate key drivers of change. In addition, the high sedimentation rates in fjords allow for high temporal resolution sampling and thus for tracing the rate of ecosystem change. Here, we will present preliminary data on one sediment core collected in Kongsfjorden, Svalbard, and one core from Masfjorden, Western Norway. Both cores cover the last three centuries with a high vertical resolution and show marine community responses to past environmental changes.