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, RCO2 = (RCO2 )0 (z/z0) b 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, b, always negative, defines the maximum curvature of the respiration depth-profile and controls the carbon flux. When |b| is large, the carbon-flux (FC) from the epipelagic ocean is 5 low and the nutrient retention efficiency (NRE) are 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 FC as well as the capacity of epipelagic ecosystems to retain their nutrients. The ratio of seawater RCO2 to incoming FC is the NRE, a new metric that represents nutrient regeneration in a seawater layer in reference to 10 the nutrients introduced into that layer via FC . A depth-profile of FC is the integral of water column respiration. This relationship facilitates calculating ocean sections of FC from water column respiration. In a FC section and in a NRE section across the Peru upwelling system we found a FC and an NRE minimum extending down to 400 m, 50 km off the Peru coast over the upper part of the continental slope. Finally, consideration of the coupling between respiratory electron transport system 15 activity and heterotrophic oxidative phosphorylation promoted the calculation of an ocean section of heterotrophic energy production (HEP). It ranged from 250 to 500 J d−1 m−3 in the euphotic zone, to less than 5 J d−1 m−3 below 200 m on this ocean section.