This study investigates year-to-year variability of mixed layer depth (MLD) and its associated chlorophyll-a concentration changes in the East Sea. Comparison between winter MLD and wind from 2004 to 2010 finds that MLD decreases (increases) in the years of weak (strong) wind. Distinct deepening of MLD in 2008 is associated with increase of chlorophyll-a concentration in some areas of the East Sea, while such an increase of chlorophyll-a concentration does not appear in some areas of the East Sea showing that surface heat flux or oceanic advection dominates chlorophyll-a concentration.