Abstract

Long-term observations from arrays of current- and pressure-recording inverted echo sounders (CPIES) in the Chukchi Sea reveal pronounced variability in near-bottom thermal and dynamical processes, as well as in subsurface ocean heat content. This variability is closely linked to changes in sea-ice conditions and the associated inflow of Atlantic Water (AW). Time series of near-bottom temperatures along the Chukchi Slope exhibit quasi-seasonal to quasi-monthly variability, with warmer conditions during winter and spring corresponding to intensified AW boundary currents and a deepening of the lower AW layer. These variations are modulated by regional sea surface height gradients and wind stress curl over the Chukchi Shelf, which regulate AW transport through geostrophic adjustment. Observations of near-bottom currents further indicate that deep near-inertial motions and topographic Rossby wave activity are strongly seasonal, with substantially enhanced energy levels during summer and fall following sea-ice melt-out. Longer-term acoustic round-trip travel time measurements between the seafloor and the sea surface, together with hydrographic observations, reveal steric warming in the Northwind Abyssal Plain over the past several years, likely associated with a weakened Beaufort Gyre and increased AW inflow. These results demonstrate that the recent acceleration of Arctic sea-ice decline exerts strong control over ongoing subsurface ocean changes in the Arctic Ocean.