Vertical flow in the Southern Ocean estimated from individual moorings

• Published in: Journal of Physical Oceanography
• Main Authors: Sévellec, F., Naveira Garabato, A. C., Brearley, J. A., Sheen, K. L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Meteorological Society 2015
• Subjects: Southern Ocean
• Online Access: http://nora.nerc.ac.uk/id/eprint/511314/; https://nora.nerc.ac.uk/id/eprint/511314/1/JPO-D-14-0065.1.pdf; https://doi.org/10.1175/JPO-D-14-0065.1

In this study, we demonstrate that oceanic vertical velocities can be estimated from individual mooring measurements, even for non-stationary flow. This result is obtained under three assumptions: i. weak diffusion (Péclet number ≫1), ii. weak friction (Reynolds number ≫1), and iii. small inertial terms (Rossby number ≪1). The theoretical framework is applied to a set of 4 moorings located in the Southern Ocean. For this site, the diagnosed vertical velocities are highly variable in time, their standard deviation being one-to-two orders of magnitude greater than their mean. We demonstrate that the time-averaged vertical velocities are largely induced by geostrophic flow, and can be estimated from the time-averaged density and horizontal velocities. This suggests that local time-mean vertical velocities are primarily forced by the time-mean ocean dynamics, rather than by e.g. transient eddies or internal waves. We also show that, in the context of these four moorings, the time-mean vertical flow is consistent with stratified Taylor column dynamics in the presence of a topographic obstacle.