Dynamic and Thermodynamic Effects induced by Parameterized Tidal Mixing on Sea Ice in the Subarctic Seas

Tidal mixing, an essential component of ocean vertical mixing, is a potential yet under-quantified factor influencing sea ice changes across the pan-Arctic domain. Although previous studies have assessed tidal impacts on Arctic sea ice by directly imposing tidal forcing, they cannot isolate effects of tidal mixing from other tide-induced processes. Therefore, by utilizing a coupled ice-ocean model with and without tidal mixing parameterization, this study quantifies the effect of tidal mixing on winter sea ice growth (WSIG) volume budget in subarctic seas and investigates the relative dynamical and thermodynamic contributions. Results reveal that tidal mixing reduces the mean WSIG (MWSIG) volume by 130.51 km³ (-9.79%) in the Labrador Sea and 63.82 km³ (-7.39%) in the Sea of Okhotsk during 1958–2018. Further analysis demonstrates that these reductions are predominantly driven by thermodynamic processes: enhanced tidal mixing significantly increases vertical eddy diffusion, which intensifies the upwelling of the warmer and saltier deep water to the near-surface, thereby, altering the near-surface thermohaline structure and inhibiting basal ice growth and enhancing basal ice melt. In the Baffin Bay, however, MWSIG exhibits a unique dynamic-driven dipolar response pattern to tidal mixing: MWSIG increases near Greenland due to the enhanced ice advection, while decreases near the Canadian Arctic Archipelago due to the weakened ice convergence, yielding a minimal MWSIG change. This study highlights the dual mechanisms through which tidal mixing exerts a non-negligible impact on MWSIG in different subarctic seas, providing new insight into oceanic regulation of sea ice.