Stable isotope δ¹⁸O dynamic fractionation coefficient between water and sea ice in the Arctic Ocean

Abstract Variations in stable oxygen isotopic compositions in sea ice provide information on environmental conditions during sea ice formation and also are important in understanding the regional and temporal aspects of the fresh water budget of the Arctic Ocean. We analyzed the oxygen isotope fractionation between sea ice and sea water using ice core and surface ocean samples obtained in a field study in the Lincoln Sea/Switchyard region of the Arctic Ocean. Using the Sea Ice Tracking Utility, we track the sea ice backward in time along drift trajectories, and use a simple model to calculate ice growth rates. Our results indicate that sea ice at the bottom of the floes that we sampled in the Switchyard Region grew within the past winter along a trajectory extending back to the North Pole. The effective fractionation coefficients from the bottom ice layers and the parent water mass are close to 2.11‰ with a standard error of ±0.06‰. Knowing this sea-ice oxygen isotope fractionation coefficient for high Arctic drifting ice is critical for use of equations for mass balance, salinity, oxygen isotopes and nutrients to calculate water mass fractions and sources to understand freshwater balance.