A subsurface chlorophyll maximum (SCM) forms where phytoplankton growth is optimized at a depth balancing adequate light from above and nutrient supply from below (often near the nutricline); a persistent, well-defined SCM at moderate depth is characteristic of stratified, nutrient-poor (oligotrophic) open-ocean waters.
In the open ocean, a subsurface chlorophyll maximum around 20-25 m depth reliably indicates oligotrophic conditions: surface waters are nutrient-depleted (low chlorophyll near the surface),...
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