Vertical Velocities and Mixing Estimated from Seagliders

Using Seagliders equipped with a standard suite of hydrographic sensors, we document a geography of vertical velocity and mixing under different stratification and forcing conditions. Vertical velocities in the world's oceans are typically small, on the order of 1 cm/s, posing a significant challenge to observational techniques. Using Seagliders, we estimate vertical velocity by differencing observed glider vertical velocity (derived from pressure measurements) from expected glider vertical velocity (estimated from a glider flight model). Further filtering of rms-velocities allows an estimation of relative values of turbulent dissipation.

Here we present a geography of vertical velocities and turbulent dissipation in the Labrador Sea: in the surface mixed layer and during deep convection, and below the mixed layer in the presence of tides and eddies. Mixing estimates are high in the surface mixed layer and during deep convection, where the relative strength of mixing scales with the intensify of surface forcing. Below the mixed layer, dissipation shows modulations of up to two orders of magnitude over the span of days. While this method does not determine the absolute values of turbulent dissipation, Seagliders equipped with only the standard hydrographic suite of instruments allow extended duration, time-varying vertical profiles of oceanic mixing.