Abstract
Continuous observation of aquatic at the ocean surface, with a sensitive response time and high spatiotemporal resolution, is essential for research into the carbon biogeochemical cycle. In this work, a portable tunable diode laser absorption spectroscopy (TDLAS) system for dissolved CO2 detection in surface seawater, coupled with a home-made headspace equilibrator, allowing real time underway measurements, is described. Both the optical detection part and sample extraction part were integrated together into a compact chamber. An empirical equation suitable for this system was acquired, which can convert the concentration from the gas-phase to the aqueous-phase. A monitoring precision of 0.5% was obtained with time-series measurement, and the detection limits of 2.3 ppmv and 0.1 ppmv were determined with 1 s and 128 s averaging time, respectively. Sampling device used in this work was ameliorated so that the response time of system reduced by about 50% compared to the traditional ‘shower head’ system. The fast response time reached the order of 41 s when the final concentration span was 3079 ppmv. For1902 ppmv, this figure was as short as 20 s. Finally, a field underway measurement campaign was carried out and the results were briefly analyzed. Our work proved the feasibility of the TDLAS system for dissolved CO2 rapid detection.
Highlights
In the special case of underway measurements, the headspace equilibrator was designed to work simultaneously with two methods of spray and bubble so that the response time of system was reduced by about 50% compared to traditional “shower head” headspace equilibrator
Our work proved the feasibility of the tunable diode laser absorption spectroscopy (TDLAS)-based system for dissolved CO2 rapid detection, and can provide a reference for other researchers engaged in marine sensor development
We demonstrated a compact deck-based TDLAS system for dissolved
Summary
The oceans, which account for 71% of the Earth’s surface area, represent a significant sink of anthropogenic CO2 emissions, making remarkable sense to global carbon cycle and in mitigating anthropogenic climatic anomalies [3,4,5]. Some 30% of total anthropogenic CO2 emissions were absorbed by the oceans [4,6] and the rate of ocean uptake of atmospheric CO2 has increased continuously for the last two decades on account of the ever-increasing concentration of CO2 in the atmosphere [7]. The anthropogenic carbon dioxide emissions have caused pronounced changes to the marine carbonate system [8], and are altering the surface seawater acid-base chemistry towards increased acidic globally [1,9].
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