Climatology of the mixed layer depth in the East/Japan Sea

A climatology for the mixed layer depth (MLD) in the East/Japan Sea was produced using temperature profile data collected from 1931 to 2005. MLD is defined as the depth at which the temperature differs from that at 10 m depth by 0.2 °C. It varies seasonally with a range of about 20 m, a minimum, near the subpolar front (SPF, 38°–41°N), 60–100 m in south of 38°N and north of 41°N, and about 200 m near the winter convection region (132°–135°E & 41°–43°N). The weaker seasonality near the SPF seems to result from year-round strong stratification sustained largely by advected warm water of the East Korean Warm Current and a result of complex dynamic process of frontogenesis including lateral dynamics or wind-induced friction. The temperature-based MLD does not show any significant difference (mostly less than 20 m) from the density-based values over most of the East/Japan Sea except a few localized regions near the Russian and Japanese coasts where barrier layers form from late fall through early spring. This study confirms that atmospheric forcing largely dominates the overall magnitude of MLD seasonal variability in most of the East/Japan Sea.

► The MLD undergoes strong seasonal variation over the entire East/Japan Sea, ranging from 10–20 m in summer to more than 400 m in winter.
► The annual-mean MLD shows a reversed bowl–shaped distribution: smaller near the subpolar front (SPF) and larger north or south of the SPF.
► The temperature–based MLD is similar to the density–based values over most of the East/Japan Sea.