Temporal variations of the winter mixed layer south of the Kuroshio Extension

A monthly mean time series of the temperature profile in the recirculation gyre south of the Kuroshio Extension has been produced for the period 1971–2007 to examine temporal variations of the winter mixed layer. The winter mixed layer depth (MLD) shows both interannual and decadal variations and is significantly correlated with variation of the mean net surface heat flux in late autumn to early winter. There is also a close relation with the strength of pre-existing subsurface stratification, measured as vertical temperature gradients in the preceding summer. Linear multiple regression analysis shows that a significant fraction of the variations in the winter MLD is explained by the surface heat flux and the strength of the stratification. The contribution of the two factors is comparable.