In this and the seven subsequent slides, one annual cycle of upper ocean variability is illustrated by imaging the temperature field and superimposing the vertical coordinate interfaces and the mixed layer base (thick line). Differences in upper-ocean temperature can be large at grid points located in frontal zones and the boundary regions between gyres. Horizontal displacement of these oceanographic features among simulations can lead to substantial T differences. In general, smaller differences are observed at grid points located at gyre interiors. The annual cycle at point NAC represents variability in the boundary zone between the subtropical and subpolar gyres.