Sedimentary organic carbon dynamics in a glaciated Arctic fjord: tracing contributions of terrestrial and marine sources in the context of Atlantification over recent centuries

Abstract. In this study, we investigated sedimentary organic carbon (OC) dynamics in Kongsfjorden, Svalbard, using three multicores collected during the HH22 and HH23 cruises aboard the RV Helmer Hanssen in 2022 and 2023. We assessed the relative contributions of petrogenic, soil-derived, plant-derived, and marine OC by applying a four-source apportionment approach based on Δ¹⁴C_org, δ¹³C_org, and lignin parameters, including the (Ad/Al)ᵥ ratio and lignin phenol concentrations, with Monte Carlo (MC) analysis. Age-depth models based on ²¹⁰Pb and ²²⁶Ra data were used to evaluate temporal variations in the accumulation rates (ARs) of sedimentary OC. Our findings revealed a significant increase in marine OC ARs in recent decades, which appears to be closely linked to enhanced Atlantic Water (AW) inflow. This trend suggests that changes in the fjord’s biogeochemical cycles, driven by AW, are influencing sedimentary OC dynamics. Consequently, the increasing influence of AW underscores the potential for ongoing Arctic warming to further amplify AW inflow into Arctic fjords, with significant implications for carbon cycling and fjord ecosystems. By providing a historical perspective on AW trends and their effects on sedimentary OC dynamics, this study offers valuable insights into the potential consequences of future climate change.