Technical note: Seamless gas measurements across Land-Ocean Aquatic Continuum – corrections and evaluation of sensor data for CO<sub>2</sub>, CH<sub>4</sub> and O<sub>2</sub> from field deployments in contrasting environments

Abstract

<p><strong>Abstract.</strong> Comparatively the ocean and inland waters are two separate worlds, with concentrations in greenhouse gases having orders of magnitude in difference between the two. Together they create the Land-Ocean Aquatic Continuum (LOAC), which comprises itself largely of areas with little to no data in regards to understanding the global carbon system. Reasons for this include remote and inaccessible sample locations, often tedious methods that require collection of water samples and subsequent analysis in the lab, as well as the complex interplay of biological, physical and chemical processes. This has led to large inconsistencies, increasing errors and inevitably leading to potentially false upscaling. Here we demonstrate successful deployment in oceanic to remote inland regions, over extreme concentration ranges with multiple pre-existing oceanographic sensors combined set-up, allowing for highly detailed and accurate measurements. The set-up consists of sensors measuring <i>p</i>CO<sub>2</sub>, <i>p</i>CH<sub>4</sub> (both flow-through, membrane-based NDIR or TDLAS sensors), O<sub>2</sub>, and a thermosalinograph at high-resolution from the same water source simultaneously. The flexibility of the system allowed deployment from freshwater to open ocean conditions on varying vessel sizes, where we managed to capture day-night cycles, repeat transects and also delineate small scale variability. Our work demonstrates the need for increased spatiotemporal monitoring, and shows a way to homogenize methods and data streams in the ocean and limnic realms.</p>

Response time correction of slow-response sensor data by deconvolution of the growth-law equation

“…This process is mainly driven by the difference in partial pressure between the two media and can be relatively slow. This results in high sensor RTs, leading to unwanted spatial and temporal ambiguities in recorded signals for sensors used in profiling (Miloshevich et al, 2004), used on moving platforms (Bittig et al, 2014;Canning et al, 2021), or deployed in dynamic environments (Atamanchuk et al, 2015). Herein, we refer to sensors with this particular design as equilibriumbased (EB) sensors and we seek to establish a robust, simple, and predictable method for correcting high RT-induced errors in data from these sensors.…”

Design and optimization of wireless in‐situ sensor coupled with gas–water equilibrators for continuous pCO2 measurement in aquatic environments

“…The LOAC system is highly dynamic in terms of carbon cycling and the effort to quantify the contribution of the LOAC‐emitted CO 2 to the atmosphere remains enigmatic. Some major challenges include limited spatial coverage and temporal frequency (Palmer et al 2015), isolated data not accounting groundwater and coastal wetland influences (Xenopoulos et al 2017), differing measuring techniques and protocols among oceanographers and limnologists that eventually lead to under or overestimations of pCO 2 fluxes (Downing 2014; Canning et al 2021). In general, quantification of CO 2 fluxes in the LOAC remains entailed with large uncertainties.…”

“…In general, quantification of CO 2 fluxes in the LOAC remains entailed with large uncertainties. Canning et al (2021) suggested that positioning multiple CO 2 sensors along the LOAC for long‐term observation could be a partial solution.…”

“…This continuous pCO 2 monitoring system consists of (1) water–air equilibrator, (2) dehumidifier, (3) CO 2 sensor detector, (4) calibration standards, and (5) data logger. This system can provide high resolution spatiotemporal data supporting satellite‐based predictive models for estimating pCO 2 and the air–sea flux (Lohrenz et al 2018; Canning et al 2021). Underway pCO 2 measurement technique has also been deployed in large rivers and estuaries to obtain the spatial variations of the amount of CO 2 gas being released to air by inland water in temperate regions (Chen et al 2008; Yu et al 2013; Müller et al 2016; Canning et al 2021).…”

“…This system can provide high resolution spatiotemporal data supporting satellite‐based predictive models for estimating pCO 2 and the air–sea flux (Lohrenz et al 2018; Canning et al 2021). Underway pCO 2 measurement technique has also been deployed in large rivers and estuaries to obtain the spatial variations of the amount of CO 2 gas being released to air by inland water in temperate regions (Chen et al 2008; Yu et al 2013; Müller et al 2016; Canning et al 2021). Studies have also shown that moored pCO 2 sensor buoy is useful for continuous in‐situ monitoring of diel variations of pCO 2 in large lakes and estuaries (Baehr and DeGrandpre 2004; Bastviken et al 2015).…”