Reassessing Radiocarbon Chronologies in Arctic Ocean Sediments Using Calcareous Nannofossil Bioevents

Radiocarbon chronologies for Arctic Ocean sediments remain widely debated due to low sedimentation rates, bioturbation, poorly constrained marine reservoir ages, and the presence of authigenic carbonate that can bias radiocarbon measurements. This debate is particularly critical for sediments overlying a regionally extensive glaciomarine diamict in the central Arctic Ocean, where radiocarbon ages approach the practical dating limit and interpretations range from Marine Isotope Stage (MIS) 3 to MIS 5.

Here we assess the reliability of Arctic radiocarbon chronologies by integrating new and published calcareous nannofossil assemblage data from the North Atlantic, Nordic Seas, and central Arctic Ocean with existing radiocarbon and oxygen isotope constraints. We focus on two key nannofossil bioevents: (i) the transition from assemblages dominated by Gephyrocapsa spp. to dominance by Gephyrocapsa huxleyi, and (ii) the Holocene abundance peak of Coccolithus pelagicus. These assemblage-based events are defined by relative abundance changes rather than first or last occurrences, making them less sensitive to sediment mixing over centimeter scales.

Our results show that the timing and stratigraphic ordering of these bioevents are broadly consistent across sub-Arctic and Arctic sites when evaluated against independent age controls. In particular, the Gephyrocapsa spp.–G. huxleyi transition occurs in sediments younger than MIS 4 in well-dated Nordic Seas records and is consistently observed above the Arctic last diamict interval, supporting a post-MIS 5 age for overlying sediments. While radiocarbon ages in Arctic cores display considerable scatter, likely reflecting mixing and diagenetic effects, the agreement between biostratigraphic markers and radiocarbon-based age estimates in multiple cores indicates that radiocarbon chronologies retain substantial utility when interpreted alongside independent stratigraphic constraints.

This study highlights the value of combining radiocarbon dating with calcareous nannofossil biostratigraphy to improve confidence in Arctic sediment chronologies and provides a refined framework for interpreting late Pleistocene and Holocene paleoceanographic records from the Arctic Ocean.