On The Vertical Structure Of Deep Ocean Subinertial Variability

Abstract The vertical structure of subinertial variability is examined using full-depth horizontal velocity and vertical isopycnal displacement observations derived from the Ocean Observatory Initiative (OOI). Vertical profiles on time scales between 100 hours and 1 year or longer are characterized through Empirical Orthogonal Function decomposition and qualitatively compared to theoretical modal predictions for the cases of flat, sloping and rough bathymetry. OOI observations were obtained from mooring clusters at four deep-ocean sites: Argentine Basin, Southern Ocean, Station Papa, and Irminger Sea. As no single OOI mooring in these arrays provides temperature, salinity and horizontal velocity information over the full water column, sensor observations from two or more moorings are combined. Depths greater than ~150-300 m were sampled by McLane Moored Profilers; in three of the four cases, two Profilers were utilized on the moorings. Owing to instrument failures on the deployments examined here, only about two years of full-ocean-depth observations are available from three of the four sites and some three+ years from the other. Results from the OOI Global sites are contrasted with a parallel analysis of three and one half years of observations about the axis of the Gulf Stream where much of the subinertial variability is associated with Stream meandering past the moorings. Looking across the observations, no universal vertical structure is found that characterizes the subinertial variability at the five sites examined; regional bathymetry, stratification, baroclinicity, nonlinearity and the forcing (both local and remote) likely all play a role in shaping the vertical structure of the subinertial variability in individual ocean regions.