Semidiurnal Internal Tides Observed on the Eastern Flank of Hanna Shoal in the Northeastern Chukchi Sea

Abstract

This paper investigates the role of semidiurnal tides in the Hanna Shoal region on the northeastern Chukchi Sea shelf to evaluate their impact on the regional shelf dynamics. The study is based on 2-year long velocity time series from five oceanographic moorings. These records indicate the dominance of wind-generated near-inertial energy during the summer season with low ice cover. However, when the ocean is fully covered by sea ice, tides dominate the variability in the semidiurnal energy band. The records reveal considerable seasonal variability as well as regional differences, where barotropic tides dominate in the well-mixed waters west of Hanna Shoal while bottom-trapped internal (depth-dependent) tides are observed east of Hanna Shoal, where stratification can persist year-round. Resulting tide-driven shear in winter east of Hanna Shoal under stratified conditions can occasionally reach the level of a Richardson number below 1 and can be as low as ∼0.25, implying the likelihood of shear instability and potentially eroding lower water column stability. This may lead to upward fluxes of near-bottom nutrient-rich Winter Water and thus carries ecosystem implications. Our study indicates that the internal tides east of Hanna Shoal are modulated by the spring-neap cycle and result from the interaction of barotropic tides with local bathymetry and stratification.