A biomarker-based reconstruction of sea ice conditions for the Barents Sea in recent centuries

Variations in sea ice occurrence for the Barents Sea since c. AD 1700 have been determined by analysis of the abundance of the sea ice biomarker IP₂₅ in three marine sediment box cores obtained from locations in the north, southeast and southwest parts of the region. Depth/age models for each core were established using excess ²¹⁰Pb activity profiles. Comparisons between these depth/age models with those reported previously for the Barents Sea, suggest that the proxy sea ice record may, alternatively, extend back to c. AD 1500—1600. Sedimentation accumulation rates and bulk densities were combined with IP ₂₅ concentrations, resulting in temporal changes to IP₂₅ fluxes, which have been interpreted in terms of sea ice variability. The IP₂₅ sea ice proxy data are also compared with other bulk organic geochemical parameters (total organic carbon and C/N ratios) and with sediment particle size distributions. The data indicate ice-free conditions for the southwest Barents Sea for the past c. 300 yr, consistent with previous reports based on historical sea ice records. In contrast, the combined proxy data from the southeast and north Barents Sea suggest variable spring sea ice occurrence on a c. 10—50 yr timescale, with reduced sea ice over the last c. 40—100 yr. In the early record, an enhanced sea ice occurrence is observed for the southeast Barents Sea during the mid—late nineteenth century, but as early as c. AD 1780 for the northern region. The outcomes of this study are broadly consistent with those obtained from ice edge position determinations derived previously from observational records. The study also demonstrates the potential of using IP₂₅ as a sea ice proxy for longer-term palaeo sea ice determinations (e.g. the Holocene) for the Barents Sea.