Metabolic balance in the mixed layer of the oligotrophic North Pacific Ocean from diel changes in O2/Ar saturation ratios

Abstract

In situ measurements were made to determine oxygen (O2) metabolic balance in the upper oligotrophic ocean from diel changes in O2 to argon (Ar) ratios. The study took place during 13-24 March 2014, at the Hawaii Ocean Time-series Station ALOHA (A Long-term Oligotrophic Habitat Assessment), in the North Pacific Subtropical Gyre. Microbial community respiration and gross O2 production, estimated from in situ diel changes in O2/Ar saturation, agreed well with those calculated using other independent methods. Net oxygen production (NOP), estimated from in situ diel changes in O2/Ar saturation, showed large day-to-day variability. However, when averaged over the entire observational period, mean diel NOP was in relatively good agreement with the estimated mean steady state NOP (9.2±9.3mmolO2m-2d-1 compared to 11.7±1.1mmolO2m-2d-1, respectively). Key Points Diel changes in O2/Ar were used to determine mixed layer ecosystem metabolism Estimated metabolic rates agreed well with other independent methods There was a net production of O2 in the mixed layer during the sampling period