Non-conservative nature of boron in Arctic marginal ice zones

Abstract

The Arctic Ocean is experiencing a net loss of sea ice. Ice-free Septembers are predicted by 2050 with intensified seasonal melt and freshening. Accurate carbon dioxide uptake estimates rely on meticulous assessments of carbonate parameters including total alkalinity. The third largest contributor to oceanic alkalinity is boron (as borate ions). Boron has been shown to be conservative in open ocean systems, and the boron to salinity ratio (boron/salinity) is therefore used to account for boron alkalinity in lieu of in situ boron measurements. Here we report this ratio in the marginal ice zone of the Bering and Chukchi seas during late spring of 2021. We find considerable variation in born/salinity values in ice cores and brine, representing either excesses or deficits of boron relative to salinity. This variability should be considered when accounting for borate contributions to total alkalinity (up to 10 µmol kg−1) in low salinity melt regions.