Sea level ( ) variability at interannual and longer periods is often interpreted as representing changes in steric height of either thermal or haline nature. The implicit assumption of negligible variability in ocean bottom pressure (pb) is, however, not always correct. Analyses of and pb records as well as data-constrained model estimates reveal several regions in the Southern Ocean of enhanced interannual variability, with pb magnitudes being at least half of those of on large spatial scales ( 750 km). The amplified pb variability is associated with the large-scale response to wind forcing in regions with typically weaker gradients of ambient potential vorticity. Despite those weak gradients, motions against them still play a role in balancing the wind vorticity input. Additionally, and contrary to the dominance of barotropic dynamics at subannual timescales, baroclinic effects gain more importance at interannual periods, and pb and variability are not always well correlated. Our results suggest a complex relation between and pb as a function of time and spatial scale, with topographic controls playing a role in several regions, and provide a cautionary tale on how to interpret long period changes in terms of subsurface ocean properties.
展开▼
