Sniffle: a step forward to measure in situ CO₂ fluxes with the floating chamber technique

Journal Article · Tue Jan 09 04:00:00 UTC 2018 · Elementa

DOI: https://doi.org/10.1525/elementa.275 · OSTI ID:1431413

Ribas-Ribas, Mariana ^[1]; Kilcher, Levi F. ^[2]; Wurl, Oliver ^[1]

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1. Univ. of Oldenburg (Germany). Inst. for Chemistry and Biology of the Marine Environment (ICBM)
2. National Renewable Energy Lab. (NREL), Golden, CO (United States). National Wind Technology Center

Understanding how the ocean absorbs anthropogenic CO₂ is critical for predicting climate change. We designed Sniffle, a new autonomous drifting buoy with a floating chamber, to measure gas transfer velocities and air-sea CO₂ fluxes with high spatiotemporal resolution. Currently, insufficient in situ data exist to verify gas transfer parameterizations at low wind speeds (<4 m s^-1), which leads to underestimation of gas transfer velocities and, therefore, of air-sea CO₂ fluxes. The Sniffle is equipped with a sensor to consecutively measure aqueous and atmospheric pCO₂ and to monitor increases or decreases of CO₂ inside the chamber. During autonomous operation, a complete cycle lasts 40 minutes, with a new cycle initiated after flushing the chamber. The Sniffle can be deployed for up to 15 hours at wind speeds up to 10 m s^-1. Floating chambers often overestimate fluxes because they create additional turbulence at the water surface. We correct fluxes by measuring turbulence with two acoustic Doppler velocimeters, one positioned directly under the floating chamber and the other positioned sideways, to compare artificial disturbance caused by the chamber and natural turbulence. The first results of deployment in the North Sea during the summer of 2016 demonstrate that the new drifting buoy is a useful tool that can improve our understanding of gas transfer velocity with in situ measurements. At low and moderate wind speeds and different conditions, the results obtained indicate that the observed tidal basin was acting as a source of atmospheric CO₂. Wind speed and turbulence alone could not fully explain the variance in gas transfer velocity. We suggest therefore, that other factors like surfactants, rain or tidal current will have an impact on gas transfer parameterizations.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE); Scientific Committee for Oceanic Research (SCOR); Inst. for Chemistry and Biology of the Marine Environment (ICBM); European Research Council (ERC)
• Grant/Contract Number: AC36-08GO28308
• OSTI ID: 1431413
• Report Number(s): NREL/JA--5000-71252
• Journal Information: Elementa, Journal Name: Elementa Journal Issue: 1 Vol. 6; ISSN 2325-1026
• Publisher: University of California PressCopyright Statement
• Country of Publication: United States
• Language: English