Abstract
Abstract. The ocean and inland waters are two separate regimes, with concentrations in greenhouse gases differing on orders of magnitude between them. Together, they create the land–ocean aquatic continuum (LOAC), which comprises itself largely of areas with little to no data with 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, and the complex interplay of biological, physical and chemical processes. This has led to large inconsistencies, increasing errors and has inevitably lead to potentially false upscaling. A set-up of multiple pre-existing oceanographic sensors allowing for highly detailed and accurate measurements was successfully deployed in oceanic to remote inland regions over extreme concentration ranges. The set-up consists of four sensors simultaneously measuring pCO2, pCH4 (both flow-through, membrane-based non-dispersive infrared (NDIR) or tunable diode laser absorption spectroscopy (TDLAS) sensors), O2 and a thermosalinograph at high resolution from the same water source. The flexibility of the system allowed for 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 of homogenizing methods and data streams in the ocean and limnic realms.
Highlights
Both carbon dioxide (CO2) and methane (CH4) are significant players in the Earth’s climate system, with 2016 being the first full year in which atmospheric CO2 rose above 400 parts per million, with an average of 402.8 ± 0.1 ppm (Le Quéré et al, 2018)
We have presented a portable, accessible, quick to set up multi-gas measurement system that can autonomously measure across the entire land–ocean aquatic continuum (LOAC)
We have tried to introduce oceanic precision and attention to detail into the field observations in inland water regions to potentially allow for measurements in regions of little to no data with a relatively cheap, fully enclosed sensor package with oceanic accuracy
Summary
Both carbon dioxide (CO2) and methane (CH4) are significant players in the Earth’s climate system, with 2016 being the first full year in which atmospheric CO2 rose above 400 parts per million (ppm), with an average of 402.8 ± 0.1 ppm (Le Quéré et al, 2018). With the oceans being a sink for an estimated ∼ 24 % of anthropogenic CO2 emissions (Friedlingstein et al, 2019), they have been under continuous observation and study, resulting in the collection of large global databases (e.g., Takahashi et al, 2009; Bakker et al, 2016). Such observations have shown both regional and/or temporal variabilities between a source and sink for CO2, yet it is typically a low to moderate CH4 source (∼ 0.4– 1.8 Tg CH4 yr−1; Bates et al, 1996; Borges et al, 2018; Rhee 2009), increasing in coastal regions (Bange, 2006).
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