Hydrographic Control on Subsurface Chlorophyll Maximum in the Northern South China Sea in Autumn

As a frequently-observed phenomenon in the northern South China Sea (nSCS),subsurface chlorophyll maximum (SCM) evolution from summer to winter remains unclear,neither the associated hydrographic control.In this study,on the basis of in-situ data of fall-season cruises in 2004–2006,we characterized the depth,thickness and intensity of the SCM in the nS CS using a general Gaussian-function fitting approach,and investigated a linkage to the corresponding ocean vertical buoyance properties.Our results show that the SCM becomes deeper,thicker and less intense offshore-wards in the nS CS during fall seasons.In parallel,a correlation between the SCM variation and mixed layer depth exists in the nSCS,and it becomes pronounced in the shelf region compared to the slope and basin areas in autumn.Physically,once warmer surface ocean and thus stronger thermo-determined stratification,the SCM layer goes deeper and becomes thicker and less intense in the nSCS,especially in the shelf area of the nSCS.Moreover,the impact of water temperatures at deeper layers on the vertical stratification exerts more consequent roles on the spatial variability of SCM,compared to surface temperatures in the nSCS.Specifically,the isotherm line of 22°C acts as crucial indicator for variations of the SCM in the nSCS during autumns.

Journal of Oceanology and Limnology