Tracking sources, sinks and long-term trends of methane emissions is imperative under climate change. Marine methane fluxes remain elusive and uncertain even though the ocean plays a major role in global budgets. High-latitude fjord ecosystems are widespread, store large amounts of sediment carbon, and undergo cycles of water column mixing, making them potential but still overlooked sources of methane to the atmosphere. Here, state-of-the-art benthic lander robots and multi annual observations revealed that anoxic fjords emit substantially more methane during mixing events than under water stratification. Fjords only cover 0.1% of global sea surface area, but may contribute as much methane as that released by the open ocean, which covers 84% of the global sea surface.

Data were collected using different methods. Salinity, temperature and oxygen (O2) were observed online with Seabird SBE911plus CTD and SBE43 oxygen sensors. Hydrogen sulfide (H2S) was analyzed according to Grasshoff et al. (2009). Methane (CH4) concentrations in the headspace were determined by GC analyses. Fluxes of dissolved inorganic carbon (DIC) in this dataset were extrapolated from Viktorsson et al. (2013). For more information regarding analyses and analytical equipment refer to the associated article and supporting information.

References:

Grasshoff K, Kremling K, Ehrhardt M (2009). Methods of seawater analysis. John Wiley & Sons.

Viktorsson L, Kononets M, Roos P, Hall PO. Recycling and burial of phosphorus in sediments of an anoxic fjord—The By Fjord, western Sweden. J Mar Res 71: 351-374.(2013).