Accurate Estimation of Net Community Production From O₂/Ar Measurements

Abstract

Under physically isolated conditions, net community production (NCP) can be accurately estimated from the rate of oxygen evasion to the atmosphere derived from local mixed layer oxygen/argon measurements. We use a simple box model to demonstrate that, when physical inputs are negligible, the sea‐to‐air flux of biological oxygen (bioflux) represents the average NCP exponentially weighted over the past several residence times of oxygen in the mixed layer. This new weighting scheme shows that there is no apparent lag between bioflux and exponentially weighted time‐averaged NCP. Furthermore, a strict steady state assumption is unnecessary to this relationship. However, this widely used O2/Ar method is not effective in dynamic coastal zones where low oxygen water upwells to the surface. Yet these zones are highly productive and their episodic productivity needs to be quantified. We use a quasi‐2‐D version of the Regional Ocean Modeling System, including oxygen and argon as prognostic variables, to explore the application of this method and the relationship between NCP and bioflux in a coastal upwelling system. We show that bioflux is an accurate measure of NCP over large regions of time and space. Bioflux is most biased near the shore following upwelling favorable winds, where bioflux is sometimes negative (flux from the atmosphere to the ocean) and even positive bioflux values can severely underestimate NCP. Assessing a range of model variables that are easily observed in the field, we show that sea surface temperature is the most effective at identifying bioflux measurements that are likely to be biased.

Spring net community production and its coupling with the CO<sub>2</sub> dynamics in the surface water of the northern Gulf of Mexico

“…The observed high NCP rates (e.g., up to 235.4 mmol C m −2 d −1 in NCP O 2 Ar , up to 360.7 mmol C m −2 d −1 in NCP DO-incub , Fig. 7c) are within the range of prior estimates for this region during the spring season (−238 to 624 mmol C m −2 d −1 , Cai, 2003;Guo et al, 2012;Huang et al, 2012;Lohrenz et al, 1990Lohrenz et al, , 1997Lohrenz et al, , 1999 and are among the highest in large river estuarine and shelf waters (Cooley and Yager, 2006;Dagg et al, 2004;Ning et al, 1988;Ternon et al, 2000).…”

Significant Biologically Mediated CO2 Uptake in the Pacific Arctic During the Late Open Water Season

“…The residence time of dissolved O 2 in the surface mixed layer with respect to gas exchange (which drives ∆O 2 and ∆O 2 / Ar toward equilibrium) is typically ~2 weeks, a function of the ratio of mixed layer depth to the gas transfer rate (k O2 ). Therefore, ∆O 2 / Ar indicates the time‐integrated net metabolism over this timeframe (Kaiser et al, ; Teeter et al, ).…”

Variations in Rates of Biological Production in the Beaufort Gyre as the Arctic Changes: Rates From 2011 to 2016

“…GOP and NCP calculated from the gas tracers provide an exponentially weighted average of production over approximately the previous 6 to 20 days (Teeter et al, ). The rates are only for the mixed layer and thus will not include any production occurring in the region between the bottom of the mixed layer and the bottom of the euphotic zone.…”