Remote Sensing of the Subsurface Chlorophyll Maximum Depth in the North Pacific Ocean

Estimation of the subsurface chlorophyll maximum (SCM) depth is critical to constructing the vertical profile of chlorophyll a, which in turn is important in accurately assessing phytoplankton distribution, especially in the extensive tropical oceans. Current ocean colour algorithms generally detect a limited area only or use a suite of environmental variables, part of which may be difficultly quantified. By using field in situ observations, a two-step approach, in which the first step used a relationship between sea surface temperature and surface chlorophyll to detect the occurrence of the SCM and the second step used an algorithm based on the ratio of remote sensing reflectance, was developed to remotely estimate the SCM depth in the North Pacific. Although this approach, with the inputs of easily available ocean colour data, is simple, the deviation in the remotely sensed SCM depth was only about +/- 17%. Our study may provide a promising approach to assess the stratification status of the water column and to help profiling the vertical variation of chlorophyll in the North Pacific and even in the global oceans.