Arctic Ice-Ocean Interactions in an 8-to-2 Kilometer Resolution Global Model
A new atmospheric reanalysis forced ultra-high (~2-4 km in the Arctic) resolution global ocean-sea ice model is used to investigate the influence of the upper ocean on sea ice during 2017-2020 in the eastern Arctic basin. In particular, ocean/sea-ice feedbacks resulting from excessive summer melt and then refreezing lead to excessive brine rejection and oceanic convective mixing, potentially bringing warm sub-surface Atlantic Water into the mixed layer and into contact with sea-ice.
Over recent decades, increasing concentrations of greenhouse gases have produced surface warming in the Arctic that is at least two times faster than the global average. Accelerated loss of sea ice has accompanied this rapid warming, both in terms of extent and thickness, with the greatest losses occurring in summer. Declining sea ice can induce ocean-sea ice feedbacks that further perpetuate sea-ice loss.
Greater summer melt not only increases upper-ocean stratification but also brine rejection from sea ice in the following fall freeze-up, overall enhancing the sea-ice seasonal cycle. In this study, we describe a depiction of “near-term” Arctic Ocean and sea-ice conditions (2017-2020) from an atmospheric reanalysis-forced ultra-high resolution global ocean/sea-ice simulation in which the horizontal grid mesh reduces from 8 km at the equator to 2 km at the poles (UH8to2). We find the simulation reproduces observed distributions of seasonal sea-ice thickness and concentration realistically, although concentration is biased low in the spring and summer, and low biases in thickness are found in the central and eastern basins in the fall. Volume, fresh water, and heat transports through key passages are realistic, lying within observationally determined ranges. Climatological comparisons reveal that the UH8to2 Atlantic Water (AW) is shallower, warmer, and saltier than the World Ocean Atlas 2018 climatology for 2005-2017 in the eastern basin. Our analysis suggests that these AW biases, combined with unrealistically low stratification in the upper 100 m of the simulated ocean, contribute to the winter biases in modeled sea-ice thickness.