The estimation of gross oxygen production and community respiration from autonomous time‐series measurements in the oligotrophic ocean

Abstract

Diel variations in oxygen concentration have been extensively used to estimate rates of photosynthesis and respiration in productive freshwater and marine ecosystems. Recent improvements in optical oxygen sensors now enable us to use the same approach to estimate metabolic rates in the oligotrophic waters that cover most of the global ocean and for measurements collected by autonomous underwater vehicles. By building on previous methods, we propose a procedure to estimate photosynthesis and respiration from vertically resolved diel measurements of oxygen concentration. This procedure involves isolating the oxygen variation due to biological processes from the variation due to physical processes, and calculating metabolic rates from biogenic oxygen changes using linear least squares analysis. We tested our method on underwater glider observations from the surface layer of the North Pacific Subtropical Gyre where we estimated rates of gross oxygen production and community respiration both averaging 1.0 mmol O2 m−3 d−1, consistent with previous estimates from the same environment. Method uncertainty was computed as the standard deviation of the fitted parameters and averaged 0.6 and 0.5 mmol O2 m−3 d−1 for oxygen production and respiration, respectively. The variability of metabolic rates was larger than this uncertainty and we were able to discern covariation in the biological production and consumption of oxygen. The proposed method resolved variability on time scales of approximately 1 week. This resolution can be improved in several ways including by measuring turbulent mixing, increasing the number of measurements in the surface ocean, and adopting a Lagrangian approach during data collection.

Can ocean community production and respiration be determined by measuring high-frequency oxygen profiles from autonomous floats?

“…Nicholson et al (2015) studied diurnal oxygen cycles in a similarly low productivity region in the subtropical North Pacific but accumulated and averaged many days in order to derive an estimate of production. In a more recent study, Barone et al (2019) were able to resolve variability in production on the timescale of 1 week in the same region.…”

“…The emergence and integration of miniaturized biogeochemical sensors into autonomous platforms have opened new avenues for measuring production. Numerous studies have used particulate beam attenuation (Cullen et al, 1992;Claustre et al, 1999;Kinkade et al, 1999;Gernez et al, 2010;Dall'Olmo et al, 2011;Omand et al, 2017;White et al, 2017) or dissolved oxygen (Caffrey, 2003;Riser and Johnson, 2008;Johnson, 2010;Nicholson et al, 2015;Briggs et al, 2018;Barone et al, 2019) to estimate production from such platforms. Riser and Johnson (2008) measured oxygen profiles with profiling floats every 10 d in the subtropical Pacific Ocean.…”

Review of Manuscript by Gordon et al.

“…There is a significant vertical temperature gradient in the study region and thus an expectation that response time would be slower in deeper water than near the surface. Barone et. al.…”

“…It sounds like there was significant atmospheric forcing. Barone et al 2019 outlines how diel O2 inventories can be corrected for air-sea flux prior to fitting a diel cycle.…”

“…Other short-term incubation approaches also are fairly commonly used and measure something closer to GPP. P2-L42: add (Barone et al, 2019) and (Johnson, 2010) P3-L67: add salinity to list of corrections P6: L67: There is temperature dependence both to molecular diffusivity and kinematic viscosity P8 L84: since tau is a function of environment it is also a function of time but treated as a constant. How does that impact interpretation?…”