A deep chlorophyll maximum (DCM) is common in the pycnocline of the offshore tropical and subtropical oceans outside of divergences as well as in temperate seas and lakes during summer. It traps the diffusive flux of nutrients into the depleted upper layers. When the DCM and the associated nutricline are situated in the top of the pycnocline (e.g. as during early summer in temperate seas), cloudiness materially reducing photosynthesis in the DCM may lead to a nutrient flux into the mixed layer. For the warm seas, with the DCM and the nutricline being usually deep in the stratified domain, it is shown here that even severe cloud cover can only be expected to lead to enhanced nutrient flux into the upper parts of the pycnocline but not the mixed layer. The same is likely for temperate seas and deep lakes during the height of the summer. The implication of irregular, enhanced upward flux of nitrate for the ratio of new/regenerated primary production is noted.