Increased exposure of the shores of Hornsund (Svalbard) to wave action due to a rapid shift in sea ice conditions

Negative trends in sea ice extent in polar regions lead to increasing exposure of the coasts to wind-generated waves and thus to wave-induced erosion. In the Northern Hemisphere, a region undergoing particularly rapid changes is the Barents Sea, contributing nearly one-fourth of the total sea ice loss in the Arctic. This work concentrates on the westernmost edge of that area: the Hornsund fjord, located in the southwestern part of Spitsbergen (Svalbard). Long-term (1979–2023) variability in sea ice and waves offshore and in the coastal zone was analyzed based on sea ice reanalysis data, wave observations at three coastal locations, and a spectral wave model. We found that sea ice concentration at the entrance to Hornsund underwent a “regime shift” in 2005, from winters with frequent compact-ice occurrence in the period 1979–2005 to almost ice-free winters in the period 2006–2023. Results of simulations with a spectral wave model calibrated to observations in ice-free periods show large biases during compact-ice events (strongly overestimated wave height and energy flux, slightly underestimated peak and energy period), suggesting significant influence of ice-related attenuation on wave conditions nearshore. These biases, combined with the sea ice and wave data, were then used to estimate the mean seasonal cycles of nearshore wave conditions in the two periods 1979–2005 and 2006–2023. The results show that the lack of sea ice in the recent two decades has led to a substantial increase in wave energy reaching the coastal zone (up to 100% between February and April), and to a shift of the seasonal maximum of that energy from late autumn (November–December) to winter (December–March). Overall, these changes indicate an increased exposure of the coasts to wave-induced erosion and sediment transport.