Quantifying tidal impacts on Arctic sea ice: An unexpected mechanism for the regional delay of summer melting

Tides are an important factor shaping the sea ice system in the Arctic Ocean, by altering vertical heat fluxes and advection patterns. Unfortunately, observations are sparse and the analysis of tides is complicated by the proximity of wind-driven inertial oscillations to the semi-diurnal frequencies. Furthermore, computational costs typically prohibit the inclusion of tides in ocean models, leaving a significant gap in our understanding. Motivated by summer observations showing elevated downward surface heat fluxes in the presence of tides, we analyzed simulations carried out with an eddy-permitting coupled ice-ocean model to quantify the impact of tidal effects on Arctic sea ice. In line with previous studies, we find an overall decrease in sea ice volume when tides are included in the simulations, associated with increased vertical mixing and the upward flux of heat from deeper layers of the Arctic Ocean, but this sea ice volume decrease is less pronounced than previously thought. Surprisingly, our simulations suggest that in summer, Arctic sea ice area is larger, by up to 1.5\%, when tides are included in the simulations. This effect is partly caused by an increased downward surface heat flux and a consequently lower sea surface temperature, delaying sea ice melting predominantly in the Siberian Seas, where tides are moderately strong and the warm Atlantic Water core is located relatively deep and does not encroach on the wide continental shelf. Here, tidally enhanced downward heat flux from the surface in summer can dominate over the increased upward heat flux from the warm Atlantic Water layer.