LAUSR

A 5-year long time series of temperature and horizontal velocity in the Arctic Ocean’s Beaufort Gyre is analyzed with the aim of understanding the mechanism driving the observed variability on timescales of tens of days (i.e., subinertial). We employ a coherency/phase analysis on the temperature and horizontal velocity signals, which indicates that subinertial temperature variations arise from vertical excursions of the water column that are driven by horizontal motions across the sloping seafloor. The vertical displacements of the water column (recorded by the temperature signal) show a bottom-intensified signature (i.e., decay toward the surface), while horizontal velocity anomalies are approximately barotropic below the main halocline. We show that the different characteristics in vertical and horizontal velocities are consistent with topographic Rossby wave theory in the limit of weak vertical decay. In essence, a linearly decaying vertical velocity profile implies that the whole water column is stretched/squashed uniformly with depth when water moves horizontally across the bottom slope. Thus, for the uniform stratification of the deep water column, the response in the relative vorticity field (ensuring conservation of potential vorticity) is also uniform with depth, leading to the observed barotropic horizontal velocity changes. The prevalent topographic Rossby wave activity is discussed in context with Beaufort Gyre spin-up, dissipation, and stabilization. Plain Language Summary A 5-year long time series of temperature and velocity in the Arctic Ocean’s Beaufort Gyre is analyzed to understand the source of water motions that occur with periods of tens of days. We find that vertical water motions are driven by horizontal flows across the sloping seafloor. The vertical motions are strongest near the seafloor. On the other hand, horizontal motions in the deep Beaufort Gyre are approximately uniform with depth. We show that these characteristics are consistent with topographic Rossby waves, which are waves associated with water moving horizontally across a seafloor slope. The prevalent topographic Rossby wave activity is discussed in context with energetics and stabilization of the changing Beaufort Gyre.