Ambient Methane Isotopologues in the Laptev and East Siberian Seas during SWERUS-C3

Abstract:

Production and destruction processes of methane discriminate among the stable isotopes of carbon and hydrogen content of the resulting molecule. The isotopic content of tropospheric methane is an important tool to help quantitatively deconstruct local source and sink dynamics of this radiatively important trace gas and constrain the regional fluxes.

Here we present a first look at an extensive set of atmospheric methane isotopologue observations during the SWERUS-C3 cruise in July and August 2014 in the Laptev and East Siberian seas. Continuous in-situ isotopic observations of δ¹³C-methane and δD-methane were made in real time during the cruise using an Aerodyne Dual Quantum Cascade Laser Isotopic Spectrometer. Methane concentrations were also simultaneously measured using an LGR FGGA analyzer. Air was sampled at four different heights from 9 to 35 m above the sea surface.

The precision for our 50 second averages of one second data is approximately 50 ppt for ¹²CH₄, ¹³CH₄ and CH₃D. Calibrations were made every 2 hours to compensate for the minimal effect of instrument drift. This unprecedented dataset of atmospheric methane isotopologues across the mid and outer Russian Arctic continental shelf seas will contribute to making more precise top-down estimations of us distinguish methane sources, to make top-down estimations of those source strengths and to constrain the modelling of the methane sources from the Laptev and East Siberian Seas to the atmosphere.