Peru upwelling plankton respiration: calculations of carbon flux, nutrient retention efficiency and heterotrophic energy production.

Oceanic depth profiles of plankton respiration are described by a power function, ... similar to the vertical carbon flux profile. Furthermore, because both ocean processes are closely related, conceptually and mathematically, each can be calculated from the other. The exponent (F_C), always negative, defines the maximum curvature of the respiration depth-profile and controls the carbon flux. When b is large, the C flux (F_C) from the epipelagic ocean is low and the nutrient retention efficiency (NRE) is high allowing these waters to maintain high productivity. The opposite occurs when b is small. This means that the attenuation of respiration in ocean water columns is critical in understanding and predicting both vertical F_C as well as the capacity of epipelagic ecosystems to retain their nutrients. The NRE is a new metric defined as the ratio of nutrient regeneration in a seawater layer to the nutrients introduced into that layer via F_C. A depth-profile of F is the integral of water column respiration. This relationship facilitates calculating ocean sections of F_C from water column respiration. In a F_C section across the Peru upwelling system we found a F_C maximum extending down to 400m, 50 km off the Peru coast. Finally, coupling respiratory electron transport system activity to heterotrophic oxidative phosphorylation promoted the calculation of an ocean section of heterotrophic energy production (HEP). It ranged from 250 to 500 Jd^-1 m^-3 in the euphotic zone, to less than 5 Jd^-1 m^-3 below 200m on this ocean section. [ABSTRACT FROM AUTHOR]