De‐coupling of net community production and new production in the euphotic zone of the equatorial Pacific: A model study

A physical‐biogeochemical model is employed to estimate rates of nitrogen based primary production (PP*), net community production (NCP*), and new production (NP) in the equatorial Pacific. The model reproduces observed vertical differences between ammonium regeneration and uptake: uptake > regeneration above 40 m and uptake < regeneration below 40 m. As a result, NCP* exceeds NP in the upper 40 m, but decreases more rapidly with depth than NP. High surface NCP* appears across the entire upwelling region whereas high surface NP is found in the eastern equatorial Pacific with a much stronger spatial and temporal variability in NCP* relative to NP. The NCP*/PP* ratio shows a larger range (0.1–0.4) than the f ‐ratio (i.e., the NP/PP* ratio) (0.1–0.3). The zonal and vertical de‐coupling between NCP* and NP is caused by the time lag between biological uptake and regeneration, and the advection of organic and inorganic nitrogen. The excess of NCP* over NP in the upper euphotic zone suggests the possibility of carbon over‐consumption in the upper ocean of the equatorial Pacific with implications for predicting sinks/sources of CO 2 .