Hans Gabathuler, Nicolas Cassar, Kuan Huang, Weiyi Tang, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Nicholas School of the Environment, Duke University [Durham], ANR-10-LABX-0019,LabexMER,LabexMER Marine Excellence Research: a changing ocean(2010), and Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
WOS:000426143100062; International audience; Because of the difficulty in resolving the large variability of N-2 fixation with current methods which rely on discrete sampling, the development of new methods for high resolution measurements is highly desirable. We present a new method for high-frequency measurements of aquatic N-2 fixation by continuous flow-through incubations and spectral monitoring of the acetylene (C2H2, a substrate analog for N-2) reduction to ethylene (C2H4). In this method, named Flow-through Incubation Acetylene Reduction Assays by Cavity Ring-Down Laser Absorption Spectroscopy (FARACAS), dissolved C2H2 is continuously admixed with seawater upstream of a continuous flow stirred-tank reactor (CFSR) in which C2H2 reduction takes place. Downstream of the flow-through incubator, the C2H4 gas is stripped using a bubble column contactor and circulated with a diaphragm pump into a wavelength-scanned cavity ring down laser absorption spectrometer (CRDS). Our method provides high-resolution and precise mapping of aquatic N-2 fixation, its diel cycle, and its response to environmental gradients, and can be adapted to measure other biological processes. The short-duration of the flow-through incubations without preconcentration of cells minimizes potential artifacts such as bottle containment effects while providing near real-time estimates for adaptive sampling. We expect that our new method will improve the characterization of the biogeography and kinetics of aquatic N-2 fixation rates.