An in situ high-speed STM (video-STM) study of Cu(100) electrodes in Cu-containing 0.01 M HCl solution is presented, resolving atomic-scale dynamic Cu dissolution/deposition processes at potentials in the vicinity of the equilibrium potential. The local removal/addition of atoms at kinks proceeds anisotropically at monolayer high steps, but isotropically at bilayer steps. This behavior can be explained by the influence of the ordered (c(2 x 2)Cl adlayer on the step and kink structure, specifically by the phase relation between the c(2 x 2)Cl adlayers on the two levels. In addition, observations of more complex effects such as fluctuations of atoms at terrace corners, the parallel growth of two (root2 x root2)R45degrees row wide steps, and deposition into nanoscale troughs are reported. (C) 2003 Published by Elsevier Ltd.