Nitrogen utilization in chlorophyll and primary productivity maximum layers: an analysis based on the f-ratio

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Abstract
An analysis was made of the relative importance of ''new'' (NO3 uptake) and ''regenerated'' (NH4 uptake) production in the chlorophyll maximum (CHLmax) and primary productivity maximum (PPmax) layers of 152 profiles from temperate coastal and ocean waters. In the majority of the profiles (90 to 152), the PPmax was shallower than the CHLmax. For those profiles, the magnitude of the f-ratio [NO3 uptake/(NO3 - NH4) uptake] was statistically less at the PPmax than at the CHLmax. These results offer support to the notion that the PPmax is fuelled largely by regenerated nutrients while the CHLmax is supported by new nutrients and is consistent with published evidence that: (1) the PPmax is an important site of enhanced zooplankton grazing and nutrient regeneration, and (2) the deeper CHLmax is at least partially a manifestation of in situ algal growth associated with the nitracline.