Cracking Arctic Sea Ice by Atmospheric Circulation

Sea ice cracks (leads) are fractures or passageways through sea ice that are navigable by surface vessels. Although wintertime sea ice leads cover less than 5% of the central Arctic and up to 30% in the peripheral seas, they contribute roughly half of the air-sea heat exchange and modulate low-level clouds. It’s known that leads are generated due to shear stresses from differential motions of the near-surface oceanic and atmospheric currents, yet their relative role in lead formation, especially during extreme fluctuations, remains unclear. Using ERA5 reanalysis and AMSR-E lead area fraction, we explored the role of large-scale atmospheric circulation over nine winter seasons (2002-2011) and found that meridional winds are responsible for the lead area fraction extremes on a day-to-day time scale. Strong northerly winds, associated with the western side of polar cyclones or the eastern side of anticyclones, transport sea ice equatorward towards an unconstrained ice edge, opening up sea ice leads. Conversely, strong southerly winds, linked to the eastern side of cyclones or the western side of anticyclones, transport sea ice poleward, compressing sea ice and closing up sea ice leads. We observed that lead area fraction peaks typically lag behind the meridional wind speed peaks by 2-4 days. While the climatic control of sea ice leads is complex, these findings suggest that near-surface meridional winds could serve as indicators for extreme sea ice lead activities, particularly in marginal seas and under a warming climate. We will discuss the implications of future Arctic sea ice lead changes driven by variations in near-surface meridional winds.