Seasonal sea ice persisted through the Holocene Thermal Maximum at 80°N

The cryospheric response to climatic warming responsible for recent Arctic sea ice decline can be elucidated using marine geological archives which offer an important long-term perspective. The Holocene Thermal Maximum, between 10 and 6 thousand years ago, provides an opportunity to investigate sea ice during a warmer-than-present interval. Here we use organic biomarkers and benthic foraminiferal stable isotope data from two sediment cores in the northernmost Barents Sea (>80 °N) to reconstruct seasonal sea ice between 11.7 and 9.1 thousand years ago. We identify the continued persistence of sea-ice biomarkers which suggest spring sea ice concentrations as high as 55%. During the same period, high foraminiferal oxygen stable isotopes and elevated phytoplankton biomarker concentrations indicate the influence of warm Atlantic-derived bottom water and peak biological productivity, respectively. We conclude that seasonal sea ice persisted in the northern Barents Sea during the Holocene Thermal Maximum, despite warmer-than-present conditions and Atlantic Water inflow. The northern Barents Sea contained seasonal sea ice between 11.7 and 9.1 thousand years ago, even during the warmer-than-present Holocene Thermal Maximum and despite warm Atlantic Water inflow, according to biomarker and benthic foraminiferal stable isotope records.