Precise continuous measurements of pelagic respiration in coastal waters with Oxygen Optodes

Abstract

An analytical setup for respiration rate measurements was developed and evaluated in pelagic water samples using a commercially available optical oxygen sensor (Optode™). This setup required the development of a gas tight stopper to connect the sensors to a 1 dm 3 glass sample bottle, precise temperature control (± 0.05°C), and proper stirring of samples. The detection limit and precision of the method was 0.3 mmol O 2 m -3 d -1 . This was similar to the detection limit for the high-precision Winkler titration method reported in field studies. When compared with the Winkler method, the Optode sensor enabled operator-independent, high temporal resolution measurement of respiration, better coverage of plankton groups and detection of non-linear oxygen decline, without the need for wet chemistry. Respiration rates measured by the Optodes showed good accuracy when compared with measurements made with the Winkler titration method (3% deviation), followed the expected temperature response (Q 10 = 3.0), were correlated with chlorophyll a and were congruent with earlier reported values in the literature. The main source of uncertainty was a necessary correction for system drift during the incubation period, due to oxygen release from the plastic components. Additionally, less stringent temperature control on board research vessels during rough seas reduced the precision. We conclude that the developed Optode system can be used to measure respiration in productive coastal waters. Samples from cold or deep waters were, however, often below the detection limit.

Uncertainty and sensitivity in optode-based shelf-sea net community production estimates

“…During calibration in a thermostatic bath the optodes used typically demonstrated a precision of ±0.3mmol m −3 . This is within the specification from the manufacturer of ±0.4 mmol m −3 and in agreement with the findings of Wikner et al (2013). Thus it would appear that the largest source of uncertainty constrained here is the large degree of variability captured within the 25 h mean rather than the instrument.…”

“…Optodes tend to drift towards underestimating oxygen concentrations (Wikner et al, 2013), which will typically result in underestimates of NCP. We re-ran our analysis, simulating a 1 mmol m −3 per month negative linear drift, which provides a pseudo-cumulative oxygen NCP estimate for the spring period of (−0.5 ± 0.8) mmol m −2 , which contrasts with our corrected value of (0.5 ± 1.0) mmol m −2 .…”

“…This buffering makes directly ob-serving changes in CO 2 difficult. By comparison O 2 can be measured accurately and at high resolution over long periods with relative ease (Wikner et al, 2013).…”

Respiratory Kinetics of Marine Bacteria Exposed to Decreasing Oxygen Concentrations

“…The lack of detailed data on aerobic respiration in low-O 2 environments restricts the understanding of carbon budgets (7) and the prediction of the development of O 2 within such environments (8). Recently, STOX oxygen sensors have been applied to quantify O 2 respiration rates in OMZs (9), and by this technique, it was possible to measure rates down to about 1 nmol Ϫ1 liter Ϫ1 h Ϫ1 , which is a level of resolution that is a factor of 10 higher than that obtained by traditional methods (10). Half-saturation constants (apparent K m values) for microbial communities were estimated from the data obtained with STOX oxygen sensors, but highly variable values ranging from 30 to 200 nmol liter Ϫ1 were obtained.…”

A calibration equation for oxygen optodes based on physical properties of the sensing foil

“…DO sensors are also frequently used on autonomous platforms (e.g., moorings, floats, gliders, profilers, AUVs, benthic landers) to study a variety of processes and environments. Some examples of studies that use DO sensors include net ecosystem metabolism (Emerson and Stump 2010;Fiedler et al 2012;Martz et al 2008;Riser and Johnson 2008), air-sea gas exchange (D'Asaro and McNeil 2007;Körtzinger et al 2004), oxygen minimum zones (Revsbech et al 2009), phytoplankton blooms (Perry et al 2008), benthic respiration rates (Frederiksen and Glud 2006;Wikner et al 2013), and lake/reservoir benthic O 2 flux (McGinnis et al 2008).…”