Microbial respiration in the euphotic zone at Station ALOHA

Abstract

AbstractMeasurements of the temporal and vertical variability of microbial community respiration (MCR) in the euphotic zone (0–200 m) at Station ALOHA were made using the in vivo INT method to constrain oxygen and carbon cycling at this oceanic site. Mean ( ± 1 SE) MCR was higher in the upper (0–100 m) (0.89 ± 0.05 mmol O2 m−3 d−1) than in the lower (100–200 m) portion of the euphotic zone (0.52 ± 0.05 mmol O2 m−3 d−1). Respiration in the 0.8 μm size‐fraction relative to respiration in the 0.2–0.8 μm size‐fraction was on average 1.4 ± 0.1. Variability in MCR was observed on both daily and monthly time scales, suggesting that respiration is a dynamic process throughout the year at Station ALOHA. MCR in the 0.2–0.8 μm size fraction was more variable than > 0.8 μm MCR. Despite significant vertical and temporal variability in MCR, the euphotic zone depth‐integrated (0–200 m) MCR was relatively constant (134.8 ± 11.8 mmol O2 m−2 d−1) throughout the period of observation. Oxygen consumption via MCR always exceeded O2 production extrapolated from 14C‐primary production estimation, assuming a photosynthetic quotient of 1.13 mol O2 produced : mol CO2 fixed. MCR plus particulate carbon export from the euphotic zone for the period November 2011–October 2012 at Station ALOHA can be used to set a lower limit of ∼ 45 mol C m−2 yr−1 for gross primary production.